I have a cheap set of Ibera. Bought it on Amazon two years ago ($45 each new). Never expected them to last this long, but they have. So this might be insight as to the quality of them. As for their mounting, haven't had any problems with it. They're adjustable and once you figure out which way the lower mount should be on (so they don't slide on your rack), you'll be fine. I use them loaded as I live on my bike. The one thing that I don't like, but this is because I have items sitting on top of the panniers, is that the top portion of each has bent forward with time. But this is due to the fact that the panniers stand above the rack edge, not like better panniers. Also, the reviews that came with these panniers included many people complaining that if they stuck their laptop in it, the bottom fell out. I haven't had that happen thankfully, but I only have clothes and light weight stuff in the main compartment. The material has held up except on the front cover of the lids on the main compartment. But not a big deal. THe one thing I would complain about is that (and I don't know if the set you're looking at has this) the nylon closure portion at the top of the main compartment has torn at the seam. And that began early on. Once the entire part goes, there's no ability to overfill it. Also, know that the "covers" which came with my set which are supposed to be waterproof absolutely aren't and I don't know how they can make that claim. Haven't used them since early in the first year (they're attached in a zippered section on the bottom). That's my review for you.
If you're not focused on waterproof and duffel bag panniers, I highly recommend Lone Peak panniers out of SLC.