So, the Tyranid Prime, The Big Baddie of all Tyranid Warriors, How can he help your amry and why take him over the other HQ Choices?
Well, Let's dive right in.
He's Infantry, with no option for wings. this can hurt a bit but is not really that big of a deal.
He's an Independant Character. This is his biggest benefit. Since he is a Synapse creature, it is a definite bonus to be able to join him to a unit of say.... Hive Guard. This keeps them in line and gives them the added bonus of ablative wounds. and a 3+ save to make those ablative wounds count for something.
So he's WS6 so can handle himself in combat, in fact in most cases if he is attached to a hive guard unit, i'd un-attach him and charge that nasty cc unit that is geting close so they can continue to do their job for another turn or 2. With only S10 and other special weapons being able to kill him he's pretty safe in CC. He also is built for CC, sure he has some ranged options, but for this guy, I'd rather change them out since he can not take any larger weapons. I'd equip him as follows:
A Pair of Boneswords and a Pair of Scything Tallons. This lets him re-roll 1/2 of his misses (on average) and any wound causes instant death on a failed LD check on 3D6. Nasty as all hell.
You can give him adrenal glands, but it's not really necessessary. Toxin Sacs are a viable option as you'd be re-rolling to wound on anything with a T of 5 or lower. Combine that with the Boneswords and you can cause a lot of damage to a squad. Especially being at I 5.
So this guy is a protection unit. no Psychics, but he does have shadow in the warp.
Use him to free up points for other selections. because 100 points for this guy is a lot less than the 280 of the Swarm Lord or the 170-300 of the normal hive tyrant.