Cutoff tools have to run enough to get the wheel hot but not too much and overheat the wheel. If you buy a good (not $15) efficient air tool, go for 1/3HP instead of 1/2, and pace yourself, you will still outrun a dremel cutting speed by 4:1 or more. Plus smaller air cutoff tools fit in tight places the cordless will not.
A small die grinder has a 2" wheel and while they lack a guard, lack the cutting capacity of the 3" cutoff tool, they are small and can get in really tight places. Smaller ones use less air but still outrun a dremel. Plus at 2" a face mask is sufficient protection if they shatter.
I have both.
Buy quality US wheels for whatever you get.
-HF
Thanks for the feedback. You mentioned going with an efficient cutoff tool. What are your thoughts on the Campbell Hausfeld XT200000 ?