My dealer sold me a BMW tank bag for my GSA. Only problem was it was for a GS. So I had to modify the bracket that holds it under the seat. After a long off road ride it is safe to say I hate tank bags. I would prefer one that fits on my rear seat or rack.
Every time you fuel it has to come off. If your doing technical riding the bag on the tank gets in the way.
I would look for other options.