Working in the electrical industry for many years and have had extensive experience with the installation of and troubleshooting Variable Speed Drives.
Commercial manufacture of these units entails many man hours and a lot of R&D dollars to get to the levels of reliability etc of these units.
Speed control of AC rotating machines is a field where the basic theory has not changed for quite some time. it seems this system of Silicon Chip design uses tried and trusted basic design theory.eg use of the third harmonic.
I would be inclined to wait and see what if any problems are caused such as hash feedback into the mains or radiated hash from unshielded cables to motors arrises before rushing out and building it.
Having said the above dont let me put you off of what seems to be a very interesting design just dont expect the same operational parameters available in a comperable good commercial unit.eg ABB,Mitsubishi,General Electric.
If price is right Approx $200 for the kit i think i would build it but would only load it to about 1Hp and connect it to a 3Phase machine, something like that used on a small metal lathe.
I hope you have found these comments usefull.
:)Bazzatron