If you get a good 90+ quality drop from a Goliath Azuridae, that's your end-game piece. They go up a little higher, but 90-anything is good enough. The 10% psi cost reduction is enough to outweigh the benefits of the psi crab.
Psi crab does give a lot of physical and electrical threshold, and a nice bit of fire threshold and resistance. And since psi haste ignores armor penalty, you can move around OK. But regen 2 is nothing, absolutely nothing, compared to 10% cost reduction. The one real advantage psi crab offers is that with high quality kevlar cloth, you can basically become immune to enemy bullets except for sniper rifles. You can get your bullet DT way over 100 with kevlar cloth and psi crab, meaning you can simply ignore firearms. But as a psi character, you should have enough ways to completely avoid getting hit that you don't worry about reducing damage taken.
