I have the Kreiga US40 (1x20L and 2x10L) and they are top quality bits of kit, totally weatherproof and very versatile.
However, I stopped using them because I found them a pain in the neck to assemble with the numerous straps etc. I was always holding up the rest of the group whenever we were packing up to go home after an event, and trying to take something out of a bag whilst stopped at a petrol station etc. took forever. Switched to an Oxford tailpack which isn't as waterproof but I can fit it on the bike in seconds, and it's a piece of cake to open it and get stuff out.
The Kreiga bags also tended to shift around a lot unless I used extra grip mesh and bungeed them down really hard.