At last time for the final HQ in the Imperial Guard codex, the Primaris Psyker. With the major changes to 7th with the psychic phase, there are a few things that change with this guy, though nothing that is too major. He is one of the cheapest pyskers in the game with access to some good tables, though my favorite telepathy is not to him. Overall this is one of the strongest support units available to the IG and will still be seen in a lot of armies.
In the change of codex's, the Primaris psyker got a but cheaper and is now 50 pts, and can upgrade to ML2 for 25 pts more. This makes him one of the cheapest ML2 psykers in the game. You can take 0-3 and like the Techpriest he does not take a FoC slot nor fill mandatory HQ requirement. He has a laspistol, frag grenades, force weapon, and refractor field, cause they'll trust those to daemon magnets but not Scion commanders! Stat wise he is WS and BS 4, 2 Wds, 2 As, and Ld 9. He can draw his powers from biomancy, pyromancy, divination, and telekinesis.
For the most part you will be taking divination, of the options its the best bang for buck and with psychic focus you'll be getting multiple useful powers. Now with the changes to how psychic powers work, I see ML2 being a much more worthwile upgrade. The reason being is for one that prescience is WC2 now, requiring more dice to cast it, so you need to be able to create more WC to reliably use it. The other reason is mainly for psychic focus benefits. At ML2 you are getting 3 divination powers, with just about all being useful.
Token ML1 psykers are just not as good as they once were, the game is about WC dice now and so you'll need every advantage you can get to bring them to the table. That is the main reason ML2 is a good upgrade to go for. Added to the additional powers, you'll find some good use for him and will get at least one power off a turn. Taking two ML2s will prob be the sweet zone, its a minimal investment in points that will pay off. Added to it is that you'll have more dice to deny with, a min of 5 so if there is a power you need to really stop, you can throw all your dice at it and hope for the best. DtW is by no means reliable, but this helps much better than two ML 1s will. If you were taking two already, its just 50 more points to invest and one that is well worth it.
The next best way to use them I think is to go with telekinesis, again ML2 rolling all on it for pychic focus. You really want number 6, not to use it every turn, but having the psychic punch. With beams being better, the primaris power is actually not bad, with the real benefit causing all units hit by it to have to count as moving through difficult terrain. Generally a lot opponents fighting IG are going to be coming at you, and slowing them down is a very important thing not to be underestimated. Telekinesis is an all around good table if you are looking for a combat oriented psyker, and with 3 powers, he'll be doing pretty well.
Biomancy may be useful, at ML 2 you get two chances at getting a really useful power. The problem with biomancy is that a lot of it targets the psyker only, and really the primaris psyker does not benefit from it like a space marine librarian would. He just isn't good enough to really warrant it. Endurance is amazing though and casting that on ogryns is actually one of the best ways to use this. The problem is that its too chancy, and building tactics around random rolls is not really the best way to go about it. If you have multiple primaris and ogryns, then going all in on biomancy can work out, it will make the bastards, especially bullgryns nearly impossible to kill. Other wise this is a situational at best table, but still something to consider.
As far as daemonology, not really the best choice, wyrdvane psykers are much better if you want to go this route, as they will be more likely to survive perils rolls and keep fighting. Your much better sticking to divination than risking your primaris on daemonology.
Pyromancy is another combat oriented table, with some ok support powers. My main problem with this table is that the primaris power is not that great. If it had torrent, then it would actually be really good, but as ti stands its a heavy flamer that can be denied and doesn't help in overwatch. Oh and hope your close to the enemy. Other wise the table itself isn't that bad, the powers on it are good, if not amazing. Its solid if you are looking for an offensive psyker, though I think telekinesis has more to offer.
Overall there are two ways to run a primaris psyker and that is in the support or combat role. Divination is the way to go for support, and telekinesis is great for the combat oriented role. ML2 is much more important now for the added warp charge to both casting and denying. A pair is your best bet, with 3 being a good choice as well. These are still really good support and have not lost a whole lot in the edition change, with only ML2 being more worth taking than before.
GG