Techmarines now take up an HQ slot, meaning that I doubt you’ll ever see one again. Their statline hasn’t improved at all, and they have the same artificer armor and servo-arm, with the option to take a full servo-harness or a jump pack. He can choose from most of the armory, though he does not have access to relics. He can take a retinue of Servitors, who can either help him fix vehicles or provide some firepower. He can also improve the cover save of any single piece of terrain in your deployment zone. I found this rule great for my Executioners, but I suspect it will be less useful with an army as aggressive as Blood Angels. I don’t expect to take many units that will hang out in cover in my deployment zone.
Honestly, I don’t see much point in the Techmarine. He is the cheapest HQ choice, but the Sanguinary Priest and a Librarian are just slightly more expensive and will bring much more to your army. You could take a Techmarine with a servo-harness and stick him inside a Stormraven to keep it in the air, but that’s a substantial amount of points to add to an already expensive vehicle for a modest increase in survivability.