Air/Fuel Performance Chips!?!?!

On Ebay, there are guys selling chips that supposedly increase horse power. I just bought one. They change the air/fuel ratios. Here is what the seller had to say about his chip:
This chip connects to the wires in between the ECU and the IAT/MAF sensor.
It will modify the signals being read by the ECU, and ultimately causing the
ECU to calculate out a better air/fuel ratio to compensate these new
signals.
Does anyone have any experience with these chips?? Are they any good or are they dangerous to use?? I'll have mine installed next week and will give everyone a report.
Here is a link to the chip's I'm talking about. I bought this first one. The second one I'm thinking about trying out as well.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=2283747036&ssPageName=STRK:MEWA:IT
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=7933194569&ssPageName=STRK:MEWA:IT

Thanks.
Steve Hulbert

I saw that too a while back, they have them listed for pretty much any car. I was unsure of the effects it would have so I just went with the cold air intake...you can find them cheap on ebay.

All they do is change the resistance seen by the ECM for the air temp to make it look like there is colder air coming in. This causes the ECM to richen the fuel mixture. Its probably not much more than a resistor in a box. It will help although not much and it will definitly lower your fuel mileage.

You can get the stuff to make one from radioshack for like under $1! Those things are junk and wouldn't put one of those on any of my cars.