there is an old saying "you get owt fot nowt" inverters are fine for low power stuff, charge a phone, laptop or even a battery charger for power tools. but if you are already using a genny then you have the leads and they run for hours. an inverter powering a large load, just try dividing the rating of the tool by 12 volts and see what sort off pull you will be putting on you batteries....and that's assuming the conversion is perfect..it wont be....I have a battery powered grinder, small at 4.5 inches and it eats batteries when used, I carry 6X18volt nicads...and they don't give a full hour,if used hard, I can recharge one using a small inverter from the cigarette lighter socket, that small inverter has a capacity of 2 amps at 220 volts output....when I checked the input from the vehicle it was nearly 40 amps.....even a good battery without the engine running wouldn't last the hour....Genny every time....just worry about the health and safety and earths another day.....so buy a gen set with an RCD output....good to go
your choice....you could get a supper deluxe system with big wires to carry the high currents and battery tools for light work...and it would look the dog's dooda's..then still need a gen set to get you out of trouble when you really need it., so spending good earned money, if you already had a genny better to stick with it....you know what you need it for......genny are poor if your stuck indoors....ventilation....but would you want to leave your vehicle running outside with the keys in, when your working inside.
Rant over....hope it helps