I have their DXP bag, the strap mounted version. As handy as their proprietary system looks, I was happy with my Blackburn rack that was already on the bike and like being able to use the trunk bag on any bike. Takes < 1 minute to mount it.

I really like the bag, very well thought out. I often carry my camera in it, and it had a lot of padding to protect it. One thing I also like is the tapered slope at the front, which leaves room for my cable lock under the seat rails.

The panniers are huge, but being the fold-up type, they don't hold their shape well when loaded and items within often float to the bottom. If you are not needing the full panniers, you can slip some narrow items into the side pouches with them. I keep the carrying strap in one of them and my camera strap in the other.