Dear Friend DPP.
Well, I use RRS BH-55 Ballhead, and can use this grip in Portrait Position by adjust the ball head at the side slot hole, But If I want to use the Flash L Grip holder, Yes, I must remove this add on grip + Arca plate, to make camera flat bottom.
The Bad thing = Add the biger body to tiny EOS-M not fit in my pant pocket any more ----Ha, Ha, Ha---But the great thing = Perfected fit to big hand like you and me.
Thanks. I have the RRS BH-55 coming soon (along with new RRS legs). And a RRS plate for the M. Hopefully it will all arrive before I leave on vacation Monday. I'll see how the RRS plate works, but I like the idea of the integrated grip.