This puzzle is, in theory, quite simple to make in that it only involves roughing out the tetrahedron shape from the square-1 (much in the same way one would make the cuts for a half truncated 3x3x3 cube), filling in the spaces, with 3mm ABS, and sanding out the round-ish shape. However, technical difficulties abound when doing this, owing to the dimensions of the internal mechanism. Careful inspection of this puzzle will reveal that the "triangular" faces are not equalateral, and the the rounds are not at all arbitrary, but instead shroud the internal mechanism.
I really should have taken some pictures when building this thing...
Size: height: ~7.8cm, edge length ~8.5cm