Jumped in a bit late here, but I'll put my 2 cents in.
I bought the Aries aftermarket rails (were $224 on ebay a few weeks ago). They look the same as the OEM, but one of the end pieces on mine doesn't tighten very well (will move if you shove it). Also, the keys didn't work the locks properly, had to jiggle them quite a while to get them to open and close.
That said, for the $150 bucks or so that I saved, I'm pleased with them. Once they are mounted they look fine. I could probably figure out how to tighten the end piece up if I spent some time on it, but it isn't going to move on its own.
One thing to watch out for is the dealers that buy the aftermarket stuff and sell it for close to the OEM price. I know GM doesn't look fondly on those who do this, but it does happen.
Now I just need to find something else to add that I can spend that $150 on.
