The psi crystal cannot use somatic or verbal components, even Surrogate Spellcasting cannot fix that as it has no appendages. It is pretty much stuck with psionic classes.
It has 4 HP at level one and is one (literally one) energy ray (sonic) from death. It is really binary at that level because anything that bypasses that hardness will pretty much annihilate it instantly and the situation looks grim leveling up. A psion 20 psicrystal has 51.5 HP on average and is thus in moderare to extreme danger from a lot of reflex targeting attacks.
As for movement the fact it can be carried helps but being solely dependent on someone else for movement means jockeying for position will be problematic or you need a very cooperative team mate. Wild Cohort is a cool idea but you would need cross class handle animal ranks and then the animal will move on not your turn so if the flow of the battle shifts you may be out of place again.
You do bring up a fair point that a psicrystal PC has some unusual problems and may warrant a *. It has a massive of pile issues for existing and is downright immune to any low level attack form not based on acid or sonic, both of which can annihilate the crystal in one blow.