My first set of panniers were a Lidl special buy. They had two plastic hooks at the top and a useless velcro strap at the bottom. I used a bungee around the middle to stop the bag moving away from the rack, and the plastic hooks at the top worked fine. The bags were showerproof without any additional protection, and included an integrated rain cover for anything more than a shower.
For the price, I do think they were good value, but there are much better bags available. I was lucky enough to receive some Ortliebs for my birthday, and they really are the gold standard - absolutely solid as a rock, with no movement at all.