20hp? Is it Too good to be true?

[Matt]

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=1872147382

they claim to advance the timing by 4 degrees in any 89+ Sentra... I tried
to explain to my friend how these are for the most part, scams, but I'm not
sure how.... What would something like this actually do? for $6.99? I told
my friend it wouldnt work in my car since I have a qr25, which has a
different ecu than an sr20... right?

Sorry for being such a newb.

Matt
'02 Sentra se-r