I got an MR3 and its an interesting cartridge IME. It has a pivoting head with up and down and side to side movement. You can block the pivoting mechanism and use it completely rigid. I've had a couple really confortable head shaves with this razor.
What is also nice is the same razor takes FII blades and the new SamraiEdge. Feather also makes other holders and most can take all their blades.
Has anyone else tried feather cartridges?
ps: I really dislike their DE blades.