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Harmonic drives - and this specific mount - been around for a few years, and there is a very nice video showing what it can do traversing a scope in a circle around the perimeter of the sun. Key points:
1. No backlash - zip, nada, none at all.
2. Extremely compact and lightweight compared to a GEM for the same payload.
3. Although the mount head is mechanically very stiff the lack of balance around the axes means significant forces are transmitted to whatever is supporting it - and these change as the scope moves. The inevitable result is flexure, which effectively means pointing errors around the sky.
Bolting it firmly to a block of concrete or granite would be the only real way to eliminate this.
4. Periodic errors are significant so for imaging at any serious focal length autoguiding is a must to deal with this and #3 above.
5. Expensive.
Great for visual, great for a travelscope (solar eclipses), Ok for short focal length imaging but problematic for long focal length stuff.
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