I have 2 in my system, and they are mostly filter feeders. But I do see them catch larger "meatier" items from the water from time to time that they munch down on.
They use their large claws for defensive purposes IME "waving off" any potential "problems" that come their way.
For the most part IME they are peaceful filter feeding crabs that are very interesting to watch when you can observe them (they hide alot). Here's one of mine: