It solves my problem just fine - power critical loads for a few days by spending $100 upfront fir the cable and 5 minutes to manually switch the load. It’s a difference between moving to a hotel for indefinite time and staying put.
Sure you can set a loftier goal and spend tens of thousands of dollars and countless hours solving it. Most people won’t though.
Sorry, what device are you using to supply power once you've flipped the switch? Sure, you can get a (legal, even) manual transfer switch and plug in a little portable generator, but if we're talking about using your car as a power source, this is not going to work.