You may want to do some basic research before advocating for cheap ebay vfd's.

Here's some reading for you... https://www.vfds.com/blog/vfd-buying-guide

https://www.practicalmachinist.com/v...7-5-hp-226174/

When converting single phase to 3 phase with a vfd, the power factor is multiplied at a minimum of 1.73 (usually doubled), when using a 3 phase vfd. ( 7.5hp motor x 1.73 = 12.975hp, next largest size = 15hp vfd)
This is commonly referred to as derating.
The only way that formula doesn't apply is if you're using a vfd specifically made to use single phase input, and those are usually smaller vfd's, generally 3hp or less.
Those "modern" cheap Chinese VFD's you speak of will often state that they have single phase input vfd's all the way up to 15hp!! .....Questionable numbers..... always look at the rated input and output current on those vfd's.
A 230v 7.5hp 22 amp fla 3 phase motor will draw around 38 amps single phase power. The 7.5hp Chinese vfd I saw on ebay had a current rating of only 20amps. ....not good.....

I did my homework and researched about vfd's quite extensively a few years ago.
I happen to have two brand new Baldor 15hp vfd's, as well as the associated line and load reactors, shielded cabling, etc..., sitting in my shop that I decided not to use on my 3 phase equipment after I got a great deal on a 20hp Phase Perfect digital converter.

I'm very aware that using a vfd can work extremely well on many 3 phase applications, particularly since you can control speed, start up, braking, etc.... but large, quality vfd's are not cheap.

But hey, if it works for you, that's all that matters.
Just don't forget, the OP was/is looking for an on/off switch, not a phase conversion system.