I had a rotozip at one time as well. Really impressed by the projects that could be done as shown at an in-store demonstration. Got mine - first time I was surprised how much that little sucker wanted to run in the stock! My straight lines were not unless I used a guide. :-( It ended up yard sale material.
I do have the Craftsman version of the Dremmel - it sits quite a bit, but was very handy to use the cutting disks to clean out tile grout! It is an option for for some detail work. Could I live without it? Most definitely. Would I buy one again? Guess it would depend upon whether or not I had a specific application for which there was no other realistic option.