He is definitely not the same type of player, but he has a knifing style of rush that helps him get into the backfield on run plays as well. He is hardly an top tier pass rusher, but he has shown significantly more ability to get after the QB than Kenrick Ellis ever has.
Probably because he's a whole heck of a lot better. In my opinion, you have to try and keep Snacks, and keep Ellis if you end up being able to afford the luxury.