I've seen those SWU certificates being "gifted" with purchase of an envelope on eBay. Do these actually work/worth the money, or is this something that would likely get my hands slapped if I showed up with it at the airport?

United has me a bit confused as well ... they were telling me the only way I can upgrade from an H class is a SWU or milage, but it doesn't say anything about H class. Will these or won't these work?

I figure if I have to pay money for an upgrade (in the form of a milage xfer), I might as well see if I can avoid using miles.

Thanks,

Super