depends on how much you want to pay. i bought a second hand oxford one less than £20 seems robust enough never got round to fitting it to a bike had it a couple of years now i store gloves and the like in it. but i have used oxford tank bags for many years and they hold together well budget but pretty robust
lots of dearer ones about personally i don't think its worth the extra money
I bought the large silver BMW tail bag that works really well.
Says BMW on the sides so you get an upgrade in cudos as well dave.
Well they copied the RT anyway
Seriously the Oxford ones are hard to beat on value.
Looking on e bay second starting at £8.