I have Erica MT20, I paid $800, it is a very good machine, but like anything else, you have to learn to use it properly. I took AEFM class.
I use it to remove the gel for backfills (90% of my business), I really didn't buy it to save me time, but for my hands. I find that I'm not as tired when I use it now. It does save some time though.
The only thing I don't like is that it kicks up a lot of very fine dust...so you need some kind of dust extractor like WTAC (www.wtac.com).
But overall I'm very pleased with it.
PS. I hand filed for 7 years, bought the drill about 1 year ago....