I own one of these, with the 10m cable. It works exceptionally better than any other option I've tried.
I don't use it on an RPi (I don't own one yet), but on my home office pc, standard "High Performance" antennas that come with retail routers and wifi devices were put to shame. I'm hoping to get the newest RPi in early 2015 to experiment with.
My home office is on a second floor, I'd put a standard antenna on an extension SMA cable and mounted on a Microphone stand (has worked well for me in the past) and pick up about a dozen nearby signals, only a third of them with 90%+ signal strength. Using the LeGuang-N120 USB antenna (with the 10m cable - I know it passes the limit, but it works) and I can pick up a dozen signals with a 90%+ strength, and two dozen others with less than that.
The major issue I had was with the driver; I had to search for it like a detective and found one that works. They also didn't ship the antenna mount, which I really didn't care too much about; I simply mounted it on a homemade stand that sits in my window.
I've tested it using XP and Win7.
Whatever people have to say about it that's negative is most likely from their own speculation or inability to find the proper driver to install it. All I have to say about the device is good things; the seller shipped it incomplete, but I worked around the issue.
I will be making a YouTube review of the device soon and will post a link to it here when I manage to finish it.
Hope this helps..