To get 12V power you'd either have to wire in a new power outlet off just the rear battery, or pull the passenger seat to access the batteries every time you wanted to use it.
Max power is listed as 540 watts, so on 12V that comes to 45 amps draw.
It's usually considered to not be a good idea to draw more than about 30 amps off the rear battery, but for short periods of time it shouldn't be harmful. The dual voltage regulator can provide a max of 50 amps of 12V, but it's never good to run anything electrical near it's max rating for any length of time. Short periods of usage aren't a problem as you're drawing off the battery more than the regulator, but it still has to recharge, and the lower the battery gets the more stress on the regulator.
If I were to do it for my vehicle and planned to use it frequently, I'd put in an Orion 70 amp converter and a 3rd battery to power anything 12V off of. That way the starting batteries aren't affected. If I had a truck without the dual voltage setup, I would definitely use the above route, especially if I wanted to run anything else 12V on the truck.
EDIT: looking lower on the amazon listing, it does state 45 amps draw