The prop does not know if it is fitted in the front or the behind. In the time of glow motors, you needed pusher because the motor could only run in one direction (and prop would run backwards if fitted wrong). With brushless motors you can choose motor direction, and you can use a "pusher" in front or a "tractor" behind if you want.
The latest ones I got (Jan2010) are of a new version. Coming with 8 different diameter shaft adapter rings. It's a great improvement, you don't have to worry about centric drilling to the needed diameter any more. Weight is 4.7 gram plus shaft adapter ring. Needs a bit of sanding to remove flash.