an alternative that can be relatively quickly swapped house to house

https://www.homedepot.com/p/GenerLink-30-Amp-Meter-Mounted-Transfer-Switch-MA23-N/301961623

expensive, but saves high $ electrician hourly cost

“This Old House” has a video on an interesting add on secondary breaker box that allows room circuit by room circuit generator power up

( not 100% sure this is the video)

https://www.youtube.com/watch?v=GLgtFCJlVFQ