Ok, I have been using the tits off this system since I got it, and it keeps getting better. I had a 1988 FJ62 with dual batteries. That was cool, and pretty easy to install. Newer cars make that type of system slightly more difficult, but way more expensive if you are doing it correctly.
I think the main benefit for this type of system for me is using it combined with a more modern power station. I have a 12v fridge plugged into a power station which is plugged into the inverter. The power station runs the fridge and a number of other things as I need it. When the power gets low, I turn on the inverter, and it recharges the power station, fast. Like, in under 2 hours. Even running it briefly can push out the life for a significant amount of time, and then I can really recharge it when I am on a longer drive between camp sites.
Take a power station out and run your house in an emergency, plug it in to recharge when it gets low and turn the dead dino juice in the LC into cold beers. For occasional use items, like air compressors, skip the 12v version and go for a 120v set up. You can really use it like a 58k dollar generator.
I know I am not being creative enough when it comes to how I use it. Cannot wait to see what smarter people than me come up with.