Gomez,
I got the Lariet 04 F150 supercrew a couple of months ago. It comes standard with the bed extender. The standard bed length in the supercrew is 5.5'. You can get it in the 6.5' (I think) bed length. With my 5.5' bed, I still can't get the preverbial sheet of plywood in the bed with the extender opened up (to beat it all, the corners of the extender are deeply beveled, like the pic on the web page you attached to your original post...reduced room even more).
The bed extender just got in my way....so I took it out and its gathering dust in the shop. Maybe I'll use it again whenever I have a mid-size load to haul...but doubt it. Anyway, I just installed a tonneau cover that rolls up to the cab. The cover hardware interferes with flipping the over, so if I want to use it, I must install it in the open position, then remove it when finished.
I would recommend you look into one of the T-bars the other guys are recommending. The Bed extender just doesn't seem to give you much more usable room at all....especially for the price.
I had already decided when I bought the truck that I would use my trailer for any long loads....thus the short bed was not an issue for me.
roger