I've used one of these (http://www.maplin.co.uk/p/130w-variable-speed-rotary-tool-and-172-piece-accessory-set-n03fy) for a few cuts in GRP panels with one of the tiny grinding discs and found it ok.

Today I put the grinding stone in to trim a little (like less than 1mm) out of a chunk of mild steel, within a few minutes the chuck was knackered... This is the second tool I had, I bust the first one the same way grinding a weld out...

I am guessing it's really a hobby tool for trimming Airfix kits and the like and I am woefully misusing it.

Should I be buying a Dremel instead, or should I be looking at a die grinder?

I tend to use an air die grinder for work and find it a lot better than a Dremel although they have their uses, problem with an air powered tool is they use a lot of air.

Die grinder is much more robust, looked after will last a lifetime.

They are mainly 6mm / 1/4inch chuck, but reducers to take dremmel size tools are available.

How about an electric die grinder?
https://www.amazon.co.uk/Makita-Gd0601-4-Inch-Die-Grinder/dp/B001ASC73E

I have an air die-grinder with carbide bits. They chew through everything.

I had the same dilemma last year.

I killed my Hafords dremmel copy trying to open out a hole in some steel.
I replaced it with a cheap no name electric die grinder which cost about about £30. (my compressor isnt up to running an air grinder)

Its been much more useful than the dremmel size tool for car related stuff.

I also got a cheap set of carbide burrs to use with it. They are much more effective than the little grinding stones.

Paul

I have one of these (Just checked and not available at this time)
https://www.amazon.co.uk/gp/product/B00KBYX200/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1
Far more robust than a dremel. I have used and abused it for over 2 years and it's still going strong. If you do purchase a die grinder be aware of the speed ratings of any cutting tool you put in it, especially flap wheels. Dont ask how I know ;-)