From what I can tell by reading these two e-bay sales is that what the "box" does is modify the IAT or inlet air temperature signal to the ECM. So, I'd imagine they'd fool the computer into thinking the air was really cold outside so the ECM will richen up the mixture. Not sure how this would gain you power unless the factory settings were too lean to begin with (unlikely).
If you're interested though, I'd suggest more research....
Please let us know what you find out.
-Eric