I had a variety of problems with adjusting it to continue to fit right. The friction lock became worthless and a lot of the hardware basically rust welds into place you can't you can't re-tighten stuff - and I live in Denver, so we're not talking humid. About $5 more in decent bolts would prevent the problem, but whatever. They didn't want to help me out, then I complained on a FB post and they sent me a brand new Pro MX. They didn't have the MX (flat black instead of gloss) when I first got it, and I like the MX better than the gloss. I like the look better and it's more scratch resistant.
All in all, I like the thing, but I have had some issues with it. You really have to keep it all tight - especially if you are bombing through stuff. Otherwise it can sieze up in the rails, the brackets can fall off, etc. You just have to keep an eye on all of the stuff and I would recommend tightening/loosening the adjustment screws every once in a while just to keep them free. Also, put some lock tite on the little white stoppers at the tailgate end of the rail. They like to back out.
Oh, and the thing is supposedly rated to hold 500 lbs (distributed) on top, but I'd never try anything close to that.