Well, I bought it, I couldn't resist really :) And I messed around with it a bit, for the novelty of the thing. So far, I can confirm the following:
1) Yep, it is indeed plastic. Not the PVC thing, but the thin plastic some toys are made of (about 1.5mm??). The only metal parts are the tension rods/washers, parts of the throw-off mechanism (the lever, the bolt and the spring), the wires and two removable metal rings (look like iron) that are fitted on the inside of the hoops.
2) The shell comes in two parts, upper and lower, and the plastic lugs (yep, plastic) kinda slot in between, right on the seam. The same goes for the strainer and the butt. There is some kind of coating on the inside of the shell which must have been white once, I guess that brings out the sparkle and makes the shell non-transparent.
3) Yep, the heads are a very thin plastic and they don't have a rim, rather they're held in place by those metal rings that fit the inside of the hoop. Both the tension rods and the string for the wires pierce the head, through factory-made holes (probably one of the reasons why this baby didn't catch on).
I'll post some photos when I can, this is certainly novel.
Alex