Last time I asked about cheap Chinese rotary axis for diy builds there wasn't anything decent on the market in that "affordable for hobby" category. Recently I've noticed some new options that utilize a harmonic drive.

For example:

https://www.ebay.com/itm/19289023686...cAAOSwGJ5cigkc

And

https://www.ebay.com/itm/22451853762...oAAOSw-iNg3sbw

And

https://www.ebay.com/itm/15440777564...0AAOSw67hgcA4C

In theory, using a 50:1 harmonic gear solves the issues found on previous belt drive and worm gear versions. I'm wondering how they are in practice?

I.e. Do they operate backlash free and with enough torque and precision for continuous 4 axis or even 3+1 aluminum milling?