Having clocked up thousands of touring miles, my take on it is:
(1) The standard BMW bag is an atrocious thing, with a next to useless map / route pocket, awkward to flop out of the way at fuel stops and 'over made'.
(2) The TT bags on the other hand are tip-top. A very good sized map / route pocket. Easy to use zips. Available in two sizes, I have both according to need. Useful elasticated cord on the outside of the bag, to hold your gloves while fiddling about at passport control or tolls. A well thought out (but very simple) removable credit card holder, great for sticking a card and payage ticket into. Useful pen / pencil holder. A good inner pocket in the 'top lid' of the bag, to keep maps and other papers separate. Easy to take on and off. Not 'over made'.
I converted both my TT bags with a Powerlet socket, which works very well, too. If you don't want power in the bag, don't bother.
PS Like tyres, underpants and helmets, every bod and their dog has their own favourites. My tip? Go and look at a few different bags or trawl through the posts on UKGSer. If you end up not liking a bag, 10-1 says you WILL sell it on UKGSer to someone who WILL be dead pleased with it.
