I had one on my skoda, I would advise against it.
The Pro's: It did give me a little more power, didn't have it RR'd but could feel a slight difference(maybe 5-10bhp). Very Cheap, fit in about 20 mins.
The Con's: Caused my temp sensor to go faulty. After a couple of month use the glue that held it all together started to degrade and it was falling apart. All it does is over fuel the car so any claim that it will give you better mpg is rubbish.
Remapped my FR at AMD last year and it was a million times better, for both pull and power, i know its 10x the cost but its well worth doing it properly.
Edit: doh! just checked the ebay link!! thought you were talking about the £40 jobbies. Why spend £400 on one of these when thats what i paid for my remap!!! Its a no brainer.