I bought mine about a month ago off craigslist for $75 but it didn't have the hardware that mounts to the bed. About an hour in the shop and the mounting hardware was done. I saw the same extender at Pep Boys (I believe it was made by Westin) for $200. If this is the extender you're referring to then there aren't any issues with its fit. I happy as hell not to have the crawl under the tonneau cover to grab stray groceries anymore :-D.
As far as how it mounts to the bed... no, the Ford bed extender has the striker bolts mounted to the bed where as the Westin mounts the striker bolts on the extender itself. The two extenders basically mount completely opposite of each other.
Here are some pics. I made the mounts in about an hour, so excuse their rough appearance. Hopefully I'll get around to making a pair that are a little cleaner. I don't know how similar mine are to the Westin mounts, but it can't be too much different.
Quite simple... the striker bolts on the bed extender slide into the mounts on each side of the bed. The striker bolts act as the pivot point. Two flat spots on the striker bolts allow the extender to slip into the mounts, but won't allow it to come free once in place.