Just in general with a Dremel..no joke, don't use one without safety glasses.
They are small, the work you use them on is generally small and it's very easy to discount what 30k RPM will do with shavings or shattered bits. Also almost a matter of practice, you wind up down close to the work with your face to keep an eye on it.
I've had one for years and years, I've had cutoff discs shatter and cut my face but had glasses on at least. I simply never use one without glasses on.
Also agreed, horrible to sharpen anything with, particularly anything thin bladed. The temper issue, the fact that a small slip will ruin a blade and it's very hard to keep an even grind with one. You could maybe use one for things like a mower blade that don't matter much and are large surfaces but an actual grinder would be far more efficient for that.
I did use mine to put a nice lanyard hole in a Mora the other day though ;-).