Some years back they offered lifetime deals for cheap with a HN specific discount code IIRC, I took it for +- $30 and I bet this got them some loyal users here. The code reportedly still worked a year ago so you might want to check it out.

As for how well it works: I use it less and less as I get more of a managers schedule, but really liked it when I was programming most of the time. I still feel like I should use it more. Way less distracting than music and good rhythm to keep your mind going.