The mount you are talking about, should only be the "bracket" that engages in the lock mechanism. Two screws under the OEM seat and transfer it to the Corbin. You may have to adjust it for the lock to work well, it does have oval holes and can be adjusted somewhat.
I have both seats, did not want to order one of them or even pay BMW prices so made a bracket, looks almost OEM.
Now for the seat....I did not pay much for mine, bought it used. No way I'd buy a new one of them. Mine has the perforated cover, Corbin has stitched foam under that.
Go read on their website about the wet butt and what could, or should be done to avoid that and then decide on the cover they seem to have options.
Also it does not have a Hi/Lo position.That's fine by me but I have shorter legs. Mine is/was rubbing on the tupperware, I fixed some of that increasing the front posts height....but still had to protect the side covers with some well placed pieces of tape.Just yesterday when I noticed more rubbing I tought I had taken care of.
Comfy enough but forced me to bring the handlebars back, something I did not want to do.
If I had money I know what I'd get, certainly not a Corbin.