[obican]

Buy several body caps instead and drill holes with different diameters on them. That'll cost you less than 10$ and you won't be giving your money to someone who is trying to get rich by inventing products nobody actually needs.

 

Also, seriously, go shoot film if you are interested in pinhole. That's where all the experimenting really is. Build your own very basic camera and you can do ridiculously long exposure shots without worrying about long exposure noise reduction etc.