Will have to search for the link where someone discusses it, but if it's similar to the CLEAR program, then all it does is let you cut in front of other people at the security lines. If you're a USAian and feel like being a rude cunt to your fellow citizens (not to mention what Cold and Q said) then feel free to throw your money away. I've only been in superhuge lines coming into the US and leaving (as a US citizens of course) so may or may not be worth it depending on where you tend to go.
p.s. I think it sounds like a great system for ppl looking to recruit domestic terrorists/spies. Find someone w/ a clean record but sympathetic views and a US passport, meet them in 'normal' places (London, Madrid, Istanbul, etc) and keep them unnoticed and unscrutinized as they come in and out of the country.
"If you were born near someplace called "The Erg of ____" you lost the lottery." - Kurt the Wise
"If you're stupid, the whole world is a dangerous place." - friendlyskies