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.
Ordering this will get you a DIY kit of pieces which you will need to assemble and sticker yourself. The puzzle is available in both white and black plastic but ordering the white parts and dying them yourself is a bit more economical. I can also offer you a fully assembled, dyed and stickered version of this puzzle for a small additional fee. Contact me directly for this service.