Make sure you get one with the claw attachment. Some don't have them.

This particular one does.

A chain break is not necessary if you have the proper sized allen wrenches to undo all your derailer pulleys and don't mind futzing around with them. Looks like you'll only have to take off one pulley from your old derailer to get the chain out of it. You'll pretty much have to mostly dissassemble your new rear derailer to route the chain, however. Make sure you reference lots of pics of rear derailers so you know how the chain is supposed to be routed.