I have a variable speed corded version with the digital screen. I have had it for about 7 years now and have used it for about everything from demilling AK kits to chopping the top off my keg for a new brew pot.
If you don't have a high end air compressor the dremil rules the day. It is a lot slower working than a full size grinder or cut off wheel or a die grinder/cut off but I have found the slower you go the less chance you have to mess something up.
I will say the only cut off wheels I use are the reinforced kind. I went through 10 building my keggle and would take them down pretty much to the shank before replacing them. I normally buy grinding wheels and cut off wheels in "bulk" because you can chew threw them so fast. I buy the elcheapo Chinese reenforced cut off wheels usually found at gun shows or harbor freight.
I also had to stop during my keggle build to let the motor cool off, it was getting to hot to hold. I suppose I will have to replace the brushes in te near future due to the abuse I give it but those are pretty cheap I am sure.
It is by far one of the most useful power tools I own.