I don't know much about generators and wiring, so this may be a silly question, but...

Since these devices require some manual intervention anyway, couldn't you accomplish the same thing just by throwing the "main" breaker at the circuit panel?

The problem I see in isolating the house from the grid (which is certainly necessary if you're going to use the house wiring) is knowing when the power's available again... and I don't see that any of these devices address that either.

But I may be missing something.