At first I thought Ghost Dog was right in that it doesn't add more than 2-4 harmonics but when I tested it thoroughly with a sine wave it showed a lot more.
Test scenario was melda sine wave generator, voxengo span pro, cubase 9.5, win10 pro. - I have to say though that you need to send quite a volume into it (!) otherwise it just produces the 2-4 harmonics.
So just 4 stars from me. The volume thing could have been described somewhere.
It does add harmonics, but, it doesn't add any harmonics past the 4th. Hopefully it will be fixed in future releases, because it's a very useful concept, but as it is .... it's mostly the GUI waveform that gets transformed.
(P.S. I'm giving it the rating of 1 only because I have to. Otherwise I wouldn't rate it at all, or give it five stars if it worked.).