I've got the smaller of the motorrad one. Its ideal for a map, and a few easy to hand things, and waterproof - which means if I'm using the map or a sat nav in it I don't have to cover the window with a rain cover (wazza point in that???...other manufacturers take note!!).
Taking it off and on again for refills is a pain (for all tank bags) ... I miss my KTM Adventure on that score