Even that rotary converter, while just fine for light start load equipment such as the lath in that video, would not work for a high load air compressor. That set-up would be a big improvement over a static converter since it would apparently allow full, or near full, power once the equipment is running while the static type would only allow about 2/3 of the rated power (which would destroy an air compressor motor
). The type of rotary converter that would be useful with a compressor would be the type that uses an idler motor in conjunction with a large capacitor bank for high start-up loads. Also since a compressor is automatic start the supply voltage MUST be wired so that power can not be turned on until the converter is running, it must be wired so that the converter has to be turned on first. If someone forgets to start the converter when using something like a lath, mill, saw, etc it's no big deal, just turn it off and start the converter, but automatic start equipment such as a compressor could be seriously damaged if it switched on unnoticed while the converter was not running. The motor would remain stalled and would most likely burn out in a couple of minutes.
This is what I was talking about when I said the compressor being discussed might be a good deal IF the buyer fully understands what he is getting into. While there are a couple of ways of making it work properly there are even more ways of seriously damaging it and use of the wrong converter, even the wrong type rotary converter, could result in a burned out motor.