I've got a pair, I've had them for over 2 years. I'm only using the left one now, the right one has only been on the bike about 5 times and looks new. The other one has been mud covered and washed many times, has had an 8-pack of 16-oz soda bottles in it once a week or so, but generally just has my lunch, phone and camera in it. It's got a hole in the bottom of the main compartment but nothing that keeps it from being usable.

It's fallen off and gone skidding down the road 2 or 3 times, but that didn't really bother it much. I think the hole came from the time that I didn't secure it properly and it swung into the rear spokes (ouch).

I think I paid < $30 for my pair, but that's been a while. Not sure if they go that low now. I think they're very good utility bags. no nonsense. The only thing I'd wish for would be waterproof, but I just put stuff in a plastic bag if that's going to be a problem.

They don't come off now because I'm using the velcro safety strap, which I was too lazy to use before. Even without it though they only came off when I hit a very large hole, or washboarding at just the right frequency to beat the hell out of the bike.