Well i tried it out and it seems to be working out great. I found a bunch of hermits off the beach and thought they were easy enough and small enough to catch and put in the tank...
Well as soon as I dropped one in there, he grabbed it and attacked just as I expected... Then I dropped a few more and MAN did this guy get greedy. He was holding like 3 crabs at a time and trying to grab more at the same time. My mantis is FINALLY full! but my tank looks like a graveyard. He must have ate atleast 5 or 6 of the crabs, and there are still five or so running around in the tank. He can have them when he wants.
Also, my LFS gave me a yellow tail blue damsel as a feeder fish when I bought him, and he's still alive 3 days later! I'm kinda glad cause it's a good looking fish and I didn't really want him to get eaten, but he seems to be getting a little too comfortable around my full mantis which is a deathwish I know whenever my mantis needs a treat. I just don't know what to feed him because I don't have any fish food and he looks hungry. He took a couple bites out of a hermit corpse but I think i'mma have to get him some food.