I think the concept of OP is very slightly easier to understand because you have a bit more freedom in the setup moves, rather than having 'insert' the piece into the M-slice. However, if you've ever done freeslice on big cube edges, you'll already understand the concept of inserting a piece into a slice. The speed difference at the end makes it so much more worth it though.
Talking of how M2 and freeslice have a similar concept, has anyone ever tried doing BLD with E2 (just do zy rotation and start inserting pieces into the FR slot)? Obviously actually doing it successfully isn't any harder than M2, but just wondering whether anybody does it.