You are right about the 22/45 having the same geometry. I think the composite frame has hurt sales with more traditional gun owners. Plus the grips are integral of the frame.
As far as function it is just like all the other MK's. The 22/45 has a magazine disconnector, it can be removed by using a MK II hammer, or a spacer (easy mod)
I milled the factory grips off my frame and added a set of 1911 grips and screws. I have done several others for guys who saw mine at the range. With this mod the 22/45 has the same width as a 1911 grip.