I'm afraid to say 'buy this' ... only because I was very concerned about my own purchase and it meeting the needs so I could follow the walkthrough.
When I obtained mine, it worked but I didn't have the same firmware as the instructions - I ended up making modifications to the instructions and updating and taking some chances. Luckily it all came easily ...
I note that as of today, Amazon was out of stock. For parts like this - try Sparkfun - they have everything, but a tad more expensive. (I get all my rPi kits there - same place I found my fart sensor!)
Here is the thread I followed. It looks complicated, but it really wasn't. I urge that you read the thread as it really helped get the right specific dongle.
