The Tetrahedral Twins could be viewed as a combination of two of Okamoto's Master Pyraminxes. It has the shape of a stellated octahedron (stella octangula). I think it illustrates some things about the symmetry of a tetrahedron nicely. The puzzle is 10cm on an edge so it is around the same size as a regular pyraminx.
I'm very satisfied with how it came out. The turning is nice and fluid, the mechanism is very stable: even when I unscrewed 3/4 screws it would not come apart.
The puzzle is a bit unwieldy to hold due to its shape. The turning is good and without problem but playing with it will take some getting used to. The only flaw is that when halfway through one of the deep cut turns, certain pieces can wiggle a bit.
If you order this model, you will get a DIY kit of the plastic parts needed to make this puzzle. You will need to supply your own screws (M3), stickers and springs for assembly.
You can also order an assembled copy of this puzzle from me directly, but this option is more expensive and it will take longer to get your puzzle.
Shapeways has recently changed their pricing making this model much more expensive. I've not yet had the time to optimize this model to be as cheap as posible. Please contact me at email@example.com if you are interested in obtaining this puzzle so we can discuss cheaper options.