Connecting this to two plugs on the same circuit won't short anything unless one of the outlets is wired incorrectly.
They're used to backfeed power to your house from a generator during power outages. Technically not legal to use, but most people aren't going to pay $1k for a proper transfer switch. They come with the caveat of 'not to be operated by fuckwits' since you can kill a linesman if you don't flip your main breaker before using them.
Should be supported. If you're already running a 5000 series CPU, there won't be any issues swapping in another 5000 series.
The only time you run into issues is if you were previously running a 1000 or 2000 series CPU and need to make the jump straight to 5000 series.