There are two sizes for the GSA. The one that you see in the brochures is the big one, but if you ask nicely there is a smaller one that has a lower top and is more suited in my opinion. I had the bigger one when I first got the bike but found it was in the way.......the dealer changed it for the smaller one which is just about perfect in my opinion. I can get a couple of cameras and all the other stuff that most of us carry no problem - it is waterproof without needing another cover and the map pocket seems to fit all the maps I want to put in it. It fits on the tank without rubbing anything and does not move arouns as some might.
I have tried all manner of tank bags on GSs for the past 18 years and always find that the BM ones work out best in the long term.