so how do they fit to the bike? do you have to put a frame on first then the luggage.......ok i admit it i'm new to the hard luggage, always used throw over soft panniers..........till i burnt a big hole in one with the exhaust....
There are two types of standard panniers plastic and metal (I'm sure there are posh names)
The plastic type fit onto metal mushrooms that perminantly screw into the frame.
the metal type fit to a frame that is perminantly on the bike... there are a few comments about it looking like scaffolding.
Pros and cons for both systems.
the plastic boxes can be expanded and shrank making the back end of the bike thinner if you arent carrying so much stuff, the downside is that there seems to be an issue with the boxes ripping away from the mushrooms - I've seen a few posting here from people who've lost them and I get the impression BMW have addressed the issue by changing the design slightly.
The metal ones are one fixed size, they seem to be more robust (I've dropped the bix on both sides with mine on and you really wouldnt know it) and are designed to be as "enduro" as the rest of the bike is

- that said I read a report when the 12GSA just came about about some guy riding one across africa and having all kinds of problems with boxes dropping of (probably just an extreme case) the real down side of the BMW metal panniers is that the corrode at the first sign of salt. Mine where fine throughout the summer and autum, but 2 day and maybe 100 miles in the winter left the topbox pitted (luck I left the panniers off) You will need to do something with them
which ever way you go, metal or plastic, I get the impression its worth getting the inner bags - especially for the metal ones as the aliminium is unfinished and rubs off on everything. I can't remember how much the panniers cost, but IMHO it was enough that they should have been finished properly - luck I got the inner bags for free.
I know that there are a lot of people who rate the metal mules here, but I think they look too industrial - sorry guys.