I recently got a US-10 (TANK harness on the way) and found it to be excellent when I used it for my bikesafe course (did not want to take the full R35 rucksack I usually use for my work commute).

It stayed totally stable on the bike and was quite pleased at what I managed to get in it

tyre pump
front inner tube
rear inner tube
torque wrench & spanners for chain adjustment.
small multitool
copies of my licence, insurance etc.

And at the end of the day I just managed to squeeze in all the extra bumf they gave out (a4 so folded in half to fit in the bag).

I probaly could have mounted it a bit further back but did occasionaly find it creeping forward so I could feel it against my back which added to being able to feel bike vibrations. Not sure if I could have used it with my R35 either like that so will have to check and posts some more pics to the thread.