Panniers with rigid back panels and precise locking fasteners may not fit some of these cheaper Al racks, such as the Topeak Super Tourist. The problem is poor design, and evidently no customer feedback.

The top rails are not located far enough outwards to vertically clear the side rails. When you try snapping on some Ortliebs or similar, they can't hang down straight. You have to bend the rigid backing to get the bottom fastener close enough to engage the side rails. It's as if the rack was designed to break the top fasteners off your pannier. I had a similar experience with an Axiom rack.

You can't easily spot this design defect from pictures in internet ads. You normally discover the poor fit 10 seconds after you try to attach a pannier, and 20 seconds before you realize the shipping cost to return a $40 rack for credit is $20. This partly explains why there are always thousands of ads for bike racks on eBay, and rarely are any of them for Tubus racks.

Tubus racks are generally properly designed to accommodate all panniers. If you go with cheaper panniers (the ones with big Al hooks), these are more likely to fit Topeak/Axiom/etc cheap racks, due to the slop in the pannier fasteners. Also, it is possible to bend the hooks to improve fit.

If you can, test before buying to ensure compatibility between panniers and racks, as well as racks and bike.