I've got the front and rear set of the GT panniers. I love 'em. One of my favorite bike accessories. The well-designed pockets significantly increase my quality of life out on the road. The fabric is strong, the zippers are beefy, and the mounting hardware is see-cure. Or so I think.

In response to the claim above, that the bags were falling off of the rack, I'll assume that the hardware was being used right, but that it wasn't in the right position for your rack. Perhaps your rack has thinner-- or thicker-- tubing than typical.

But the Arkel bags are very easy to alter. Notice that the locking clamp is just a metal wing that pivots on a bolt. With two wrenches and two minutes of free time, you can unscrew the bolt, and remove the clamp. Then take a drill, and make a new hole wherever you need the clamp to be. Replace the bolt and wing. There, you're set. Now you've got rock solid mounting, good for years of bumpy rides, simple and secure.