It is best not to eat.

Almost all of the crayfish's organs are concentrated in the head, including the stomach, liver, heart, a pair of spermathecae/ovaries, the excretory organ tentacle glands, and the bladder and excretory orifices.

In short, eating the head of a shrimp is the same as eating shrimp feces, semi-digested shrimp food, and drinking shrimp urine.