I'm not sure why some people have had problems, but for me it was a fantastic solution to my girlfriends connection problems on her Macbook. It kept losing connection or having just very very poor connection when ever she was further than 5ft away from the router.
This was easily installed (by her, and she's actually terrible with computers) and at first told me it hadn't worked. So I had a look at it
Two things I noted which other people should know:
If using a Macbook, make sure to turn the airport off. Otherwise the airport and the Edimax will attempt to connect at the same time and neither of them will work. (This was why it didn't work for her)
Second, some times it says its connected, but its not. Just make sure you put in your WAP key every time you turn you computer back on.
All in all, its solved the connection problem, and even from upstairs the signal is always above 80% and is noticeably faster.