Interesting. It looks like its main caveat is that it requires javascript be enabled on a browser in order to tag the hit as "human." This is probably not a huge problem these days what with so much of the web being web-2-ified, though I think it would exclude some of my more paranoid readers.

I think it might be worth $30 though. It's a flat $30 fee and then you install it on your website, right? Not a subscription cost per month?