NIST has also just released its own article about the redefinition: https://www.nist.gov/si-redefinition/kilogram-kibble-balance

It has quite a few details that give a sense of the engineering challenges involved.

- The Kibble balance has a weighing mode, and a calibration mode; the two are used to cancel out a significant portion of the systematic error introduced by the mechanical system

- Measurements are made in a vacuum to eliminate effects of air buoyancy, which are significant at the desired level of precision.

- One advantage of the wheel configuration is that it allows the supporting cables to move the coil exactly vertically, thereby avoiding the undesirable sideways motion that a coil suspended from a beam balance can experience.

I could go on, but this gives an idea and you can go read it yourself ;)