Which model of REI panniers?
Ive seen a couple of their brand bags in store. I wouldnt use either for any sort of multi-day riding, but there probably isnt anything inherently wrong with them. The Deluxe version just seemed more like a commuter pannier. It had a lot of padding and some interior compartments for pens/papers/etc etc.
For $90, there are a lot of non-Ortlieb panniers which are capable.