I don't understand the need for creating their own currency (the "buttons" system). I hope it's something very smart, because these "exchange used goods" enterprises often fall prey to the venerable Gresham's law:

http://en.wikipedia.org/wiki/Greshams_law#Application

I.e. in this case the danger would be that users have an incentive to glut the system with low quality items (defects, uncomfortable etc.).