Mantis Shrimp

[workn2hard2day]

What is the down side to having one (about 1 1/2") in a tank that only houses 2 clowns & an anenome, a couple of crabs and a couple of snails?
I finally found him, and have taken him & his rock and placed it in the salt water mix tank.
Trying to decide his fate, I will stick him back in the tank if the only bad thing he will do is eat a snail/crab or two.
Any advice appreciated.