I have had a Dremel for many years as well as a Foredom high speed (up to 22,000 rpm) bench grinder with a flexible shaft attachment.
A while back I also got a Foredom hanging unit (like used by jewelers).
Foredom is more heavy duty than Dremel.
The Dremel I have, while there is a built in sliding rheostat, has a low speed of a few thousand rpm. That is TOO FAST for many things like sanding or rust removal from small areas.
For some things the hanging Foredom is FAR better and for some things NOT having the flexible shaft is an advantage (like cleaning my motorcycle wheels).
As Bill DeShivs mentioned, getting a sewing machine foot pedal is a good idea. They show up sometimes at our "transfer station" and I have been using one with my Foredom flex shaft. It works great and can be used as slowly as desired. I found for a lot of things, slow IS good.
Peter