This list is the first time that I've given these guys an aegis defense line. It's not a new or unique tactic by any means but it's something I've tried to avoid before. These guys are pretty hit and miss to be honest. An army such as the one Matt fielded against me will always make the static firebase seem better. If your opponent has to come close to do damage then the sheer volume of firepower will make him wish he didn't need to be so close. I can't say I'm a huge fan of the playstyle that this combination forces me into. My favourite armies are always the ones that take the fight to the enemy. I'd rather be pro-active and reactive.
There's no denying they're a powerful combination but if you've got to go and take objectives then you're going to struggle to get the most out of them. This is why I take a Devilfish for one of the squads. In an otherwise foot list you might think it would be priority target but a lot of the time I find it gets ignored. In an objective game most opponents with sense would try and take it out ASAP but on the other hand the kind of firepower needed to shift an AV12 vehicle with a 4++ save is the same kind that is needed to bring down the riptides. Target priority becomes difficult and that's why it still works. Obviously the devilfish is great for getting Fire Warriors onto objectives late on but it's also good for protecting them from flamers such as those from heldrakes or dreadknights. Finally, there's still some merit in the "Fish of Fury" tactic whereby you deliver all that S5 goodness into an enemy unit that you otherwise couldn't reach.
It isn't all that difficult to counter the fire warrior blob. They die to the same kind of thing that guardsmen do. Obviously they're got a 4+ save (and 4++ from the aegis line) but they're still only T3. Assaulting them is difficult with the obscene amount of supporting fire but staying outside 15" is the best bet if possible. The Ethereal is obviously the lynch pin. Armies that have some way of sniping him out of the unit will find the blob quickly falls apart once he's gone and there's a bonus VP into the bargain. Losing Ld10 and being close to the board edge means the fire warriors can be cleared up pretty sharpish after he's gone.
Kroot
Obviously they aren't the deadliest of units with S4 shots and S3 attacks but picking off weak objective holders like guard or cultists is easy for them. The main thing is, despite their low cost, they can't be ignored by your opponent. The key is to deploy your objectives with them in mind. Give them chance to Outflank straight onto it and preferably give them a forest to hide in and you're golden.
On occasion my kroot have even been known to down vehicles or even flyers by getting rear armour shots and rolling a few lucky 6s.
Commander and Bodyguard Team
Of course, combined with the kroot, this is a reasonable chunk of your forces in reserve but deep striking is usually the best way to go with these guys. There's a 1 in 6 chance you'll the warlord trait that prevents scatter meaning deadly accurate placement for them to do the most damage. There are very few units that shouldn't fear them. The team has 9 relatively high strength and low AP shots. If you can get them markerlight support this can mean killing off a whole unit of terminators or downing something like a dreadknight without breaking a sweat. Kills like that are nearly always game changing and for that reason this is easily my favourite unit in my list. They're only just shy of 285pts and can easily make their cost back.
If you're facing a lot of armour then the commander can use his target lock and BS5 to deal with one vehicle on his own whilst his bodyguard take out another. AV13/14 is a problem for most Tau lists and this is my solution. Very few armies can do anything to stop them from taking out a crucial unit. Once they've done their damage they can use their thrust moves to get them out of harm's way. Should they get charged then you can tank the hits on the commander's 2+ save and they've got 10 S5 attacks back to boot. They've then got a 50:50 chance of Hit & Run for an opportunity to break off and gun down their assailants. Obviously power fists aren't their friends.
In terms of equipment you might consider a shield generator for the commander but personally I think Hit & Run is more useful. The bodyguards have twin-linked fusion rather than plasma because it's often vital that those melta shots hit. Against vehicles the plasma is significantly weaker so it's still better to boost the melta and it's also handy for overwatch. Don't forget the commander has precision shots so he can occasionally be lucky enough to snipe a character.
Speaking of which one of the warlord traits allows him to prevent Look Out Sir! rolls. This makes him extremely effective. In fact all of the warlord traits are good. You can also get re-rolls of 1s to hit for a phase, 3D6 thrust moves, skyfire for a turn or no scatter on deep strike which I've mentioned. The only one that isn't all that useful is the getting up from gone to ground but could still find use when your fire warrior blob is hiding behind the aegis line.
Missile Pod Team
There's 12 missile shots (4 of which are twin-linked) and the PENchip gives them Monster or Tank Hunter. They're excellent for dealing with wave serpents as they can often cause enough pens/glances for it not to matter if the Eldar player converts the pens to glances. S7 isn't amazing for anti-tank though and indeed my team struggled against AV13 in the Necron game. However, there was some astonishingly bad luck on my part to not roll more 6s. Against MCs they're great for forcing armour saves and Monster Hunter means they'll force a lot.
Like any unit in my list, if you can get them some marker hits then they can be lethal to whatever they target. Let's not pretend they're all that amazing though. They're vulnerable to a lot of things and anything that can kill 6 marines can take them out too.
Riptides
One thing that people forget though is that they can't actually fire both weapons in the enemy turn. Every rule that would allow it e.g. Monstrous Creature and Multi-tracker, specifically states Shooting Phase. This means you have to choose between main gun and melta. Not usually a difficult choice though as terminators want a pie-plate and flyers want melta. Against AV10/11 flyers you might consider the 3 S7 AP2 shots, especially if you failed to Nova for two melta shots. Although.... now I read it in the codex it does say "fire twice this turn" which means you can't actually fire twice when Intercepting.... oops! Mind you it does say the effects last until the next Movement Phase so its somewhat ambiguous.
Even so the riptides are formidable and often difficult to deal with. Their presence is enough to distract an opponent from their game plan. Deep striking out of sight, bringing a flyer in out of range or choosing not to reserve a unit can dramatically effect how an enemy army performs.
They aren't without their downsides though. I frequently fail their Nova rolls for a start and it's a brave (or desperate) man who uses the reactor with a single wound left. Being BS3 doesn't help matters either and without marker support they can struggle. They can be great in combat against some opponents thanks to T6 but most of the time they die before getting to strike even with a 3++ save.
Pathfinders
I always try to deploy them as far from each other as possible so that an opponent is unlikely to be able to deal with two at once. Against an opponent who's familiar with them they don't usually last long but with riptides and crisis teams as distraction it's amazing how many times they do survive.
My tips for using them are firstly to remember that they have Scouts. This is great for getting them into line of sight on something for their first turn or for getting them into cover that was just outside your deployment zone. Secondly, I sometimes use them for cheeky markerlight hits on flyers to allow a unit to hit on 5+ (a 6 man unit should get one hit on a flyer). If you've decided to do this you can use that turn as a good opportunity to reposition your pathfinders as they'll be firing snap shots anyway.
Conclusion
I've been playing this list (or a very similar list) for a little while now. Whilst I'm under no illusion that a lot of my success with them is because they're from arguably the best codex around at the moment, I do think I use them somewhat differently to a lot of people. However, whenever I use them I'm always frustrated about how static they are. It isn't much fun to play against and not is it much fun for me.
I'd therefore like to make my army a little more mechanised. It's not difficult to spot that I haven't used any heavy support slots. Having a crisis team in place of broadsides is the first step to a more mobile cadre. Skyrays have to be pretty static too so I'm not likely to use them. Hammerheads are a potential but my lists are usually pretty tight on points so 195 for Longstrike is a bit much and even a basic hammerhead is a big investment.
With an emphasis on infantry based lists in the current meta (except serpent spam Eldar), the majority of lists have gotten very good at dealing with infantry at the expensive of anti-vehicle fire. I'd therefore like to get some devilfish with d-pods into the list to try and make my fire warriors a lot more agressive. To afford this I'd need to ditch the Ethereal and one squad of fire warriors. This dramatically reduces my anti-infantry fire but I gain a lot more flexibility. My fire warriors can spend more time shooting once they've gotten into a forward position and having two extra devilfish and extra drones means several units which can fire at different targets.This new approach may not be as deadly but the core of the army is still there and the big hitters are unchanged. It will mean better opportunity for scoring, more protection for the fire warriors and generally a list that's more fun.