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.