I bought and installed a square D interlock plate for the 200A resi panel in my home. Generator is a 13kW mobile PTO unit plug and cord connected using bus drop cable. Installed a 50A breaker in position 2 and have never looked back - it's great. AHJ passed it on inspection first time without issue. Total cost was $45 plus $11 for the breaker. On the switch rated question, the instructions specifically say to turn off all individual breakers, energise the 50A back-fed breaker once the PTO is interconnected and running, and THEN energise the individual branch circuits you want to use (this was the major motivation for me to use this route - I wanted to control which circuits to use). So if you are following instructions the breaker is not used to switch the load. In any case if it's rated at 50A why couldn't you use it for emergency switching (not like it's being used often), it's rated for 50A.
