I have a harmonic driven mount by a boutique Japanese maker. They do have the benefit of taking a heavy payload without counterweights with no backlash.
Here's mine in action, as you can see the motor is very silent :-
https://youtu.be/u7bpXuwFqKI
Harmonic Drives to have high PE however, and guiding is a must. RainbowAstro is coming up with a new RST135E (with encoders) and will need to see how it performs after it's released. I gather if that is successful we'll start to see encoders for their upper range too.
HobyM Crux seems more popular in the Asia/Japan region but hasn't made much traction in the western markets. Their Crux Traveler 140 was unfortunately plagued with poor QC that approx 30% had a bad batch of strainwave geared motors. Cuiv, The Lazy Geek (Youtube) was an early adopter of the Crux Traveler and encountered the issue however it seems HobyM didn't take the issue seriously till many months later.
If you're going to stick to the harmonic drive approach, I'd personally look more towards RainbowAstro which seems to have greater traction - therefore leading to larger R&D budget for RainbowAstro to invest in, as such seeing the likes of incorporating the Renishaw encoder (RA only) into their RST135E.
All in all though, harmonic driven mounts for astrophotography is still very much in their infancy. Adoption rates are slow although increasing (primarily with the RST135). Maker offerings are also increasing, although I feel they're merely testing the waters. Aside from RainbowAstro and HobyM, you also have SS-One (mine), K-Astec, even
GOTO Japan with their MX-HD.
I wouldn't (and don't) rely solely on one harmonic driven mount. I have a traditional GE mount, and the SS-One Traveler to play with.