Mine learned over time just to go to the body of the crayfish and he would bite off the entire tail section. He would then proceed to eat the tail and when he was done the front part had died off so he could eat that as well without having to worry about the pinchers. Fun fish to own.
99% of fahakas will not really allow for long term tankmates to be very honest!
From passed experience once they reach around 9-12” they can start getting aggressive towards tankmates as they learn that they are the boss...
Infact, i’ve even heard of 10+ year old fahaks who lived witb tankmates all their life, turning on tankmates over night killing everyone in sight...
So if you want a puffer of any sort, you should expect it to be a solo wet pet, coz even the friendliest of them (C.Asellus or T.schoutedeni which can somewhat be kept together) can be nippy towards tankmates...