what is this?

hello.
i was flicking through ebay looking for a fresh set of mats for my little car when i came across this item

ebay link (http://cgi.ebay.co.uk/TOYOTA-CELICA-MR2-YARIS-SUPRA-AVENSIS-20-BHP_W0QQitemZ8053800877QQcategoryZ72205QQrdZ1QQcmd ZViewItem)

my question is, what is it?
what does it do, how does it do it, does it work etc etc.
i'm of the old school of belief where if it sounds too good to be true, it probably is, so guys, what can you tell me about this (and possibly other versions of the same thing)?

Its snake oil. 5 pounds for 20hp? And they say it fits 99% of cars? I'd run away. Especially because they don't even tell you what it is!

Its a resistor that makes your car dump more fuel into it. Decreases gas mileage, does nothing for performance, and makes a nice black smoke come out of your exhaust.

A ford ranger guy dynoed with that and lost 20 whp and 15 wtq.

Btw, at the national SVT Contour meet this may, we'll be dynoing that just to see the hp losses for ourselves.

rule of thumb for anything on the internet: if it sounds too good to be true, it probably is. it's like $5 and they say you gain what, 10-20hp. you'd be lucky to get that from a full exhaust system on a civic.