They've been said to eat bristle worms and peanut worms; however, when I had one for about 6 months (then gave it to a friend as a Xmas gift, still a live with her), he ate leftover frozen food and flakes. They are anecdotally alleged to fight with other shrimp, and I couldn't say whether it's true because I never had any.
To be sure: they get BIG, FAST. That's just something to keep an eye on.