Dave if you want it to charge batteries have a look at the dc output. It's only 5amps, so at 12v that's only 60watts.
Also the output is usually 12.0V or close to that, which will not actually charge a battery.
Edit (I haven't actually tested the 12v output on a kings one but most gens are similar)
If you want it to run a 240V battery charger from it to charge batteries then that would be a better idea.
Aside from that, I've come across a few 4wheelers who have them and sporadically use them as they mostly get frowned on at camp areas.
Have asked a few questions on them and haven't heard anything bad, but most have only used them a handful of times, they are pretty noisy though. That's why they haven't been widely accepted by campers.
I have heard a few people having problems with kings products, but the store has a good policy on replacements, (at least the vic one does).
So just give it a good test out while it's under warranty.
I'd be more inclined to buy from a shop than ebay.