I read their FAQ and the SNES cable does not work for Gamecube, though they are hoping to one day make a component GC cable based on the official cable.  As for the SNES and Gen cables themselves, they only output 240p for 240p signals which a lot of tv's have trouble with.  Though not an ideal solution,  I think it's a neat project and a good, cheaper solution for better PQ for those who just play SNES or Gen.