I like the Topeak bags because I can expand the storage space as needed and the QuickTrack system is just slide and click for easy on/off compared to messing around with velcro straps. The only issue are :
- the plastic QuickTrack bottom on the bag will rattle against the metal channel on the rack on really bumpy trails.
- You can only use this bag with Topeak racks with with QuickTrack system because there are no straps. They do make the same bags with velcro straps only if you need to move the rack bags to different bikes without a QuickTrack rack.
An added plus is the QuickTrack tray runs the same length as the rack bag and acts almost like a rear fender. I ended up removing my Radrover seatpost fender because of the Topeak Rack (and the RR seatpost fender rattled too much under the rack).