My experience with the cover has been a mixed bag, partially because of choices I made, and partly because of material quality.
I recently noticed that the cover was rattling (which it didn't do before), and found that one of the little rollers that support the cover when it rolls along the rail had a seized bearing. This had caused this part of the cover to start rattling. The movement had already caused a lot of material in the rail to be worn away.
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To Retrax's credit, they immediately scheduled a new rail to be sent to me under warranty, so thumbs up there. It still does concern me that the metal they use for the rail is that soft. Especially since this is the same rail that would have to hold the Yakima rack and whatever I carry on it.
As far as choices I made:
I still like the concept of the cover, and the security that comes with it for items stored in the bed. What I hadn't realized is just how big the canister is that holds the rolled up cover. I still like the fact I now have an accessory rail on the bed, but I am not sure trade off of the lost space in the bed is worth it.
On my previous trucks I always had a soft (Access) cover. Not as secure and no rail, but did leave the whole bed available for cargo.
So: a good cover that's mostly waterproof (except at tailgate, like most covers), backed by a good warranty. You have to decide how much space you're willing to give up, and how concerned you are about metal quality for the rail.