I see M as a whole lot of effort trying to optimize something that is really not that interesting, complex or really very hard. I look at the M language, the way that you worked with, the tooling and the API and I would fully agree that it is a nice parser generator.
What it is not, I have to say, is a DSL toolkit. It is just one, small, part of building a DSL. And, to be perfectly honest, M is the drag & drop of DSL.