i have a small (2.5 inchish) unidentified smasher mantis in my 60 gal. he has been in there since the get go - almost 2 years. he is fairly timid with the fish, and the fire and cleaner shrimp - i am sure i have lost some clean up crew to him - i have lost more overturned snails to hermits than to him - i do target feed him a hunk of seameat (silversides, shrimp, etc) once a week, he will show his face at feeding time when he is hungry. i have 2 false percs, a blue sided fairy wrasse, 2 green clown gobies, a purple firefish and a jawfish - 2 cleaner shrimp and 6 fireshrimp that have been in there with him pretty much the whole time.
I tried to get him out with various traps, but failed - so i decided to leave him there. Keep in mind not all mantis of the same species have the same personality, but this one works for me
My onlyl regret is that i dont get to see him as much as if he was in a smaller species tank
just my .02 cents worth...