They're just overpriced batteries and an overpriced inverter in an overpriced box.
Plus, they're only good until the batteries run low. Unlike a generator, you can't just refill the gas tank, pull the cord, and have power again. The batteries need to be recharged, and that takes hours when you have mains power available. A little fold-out solar panel you set on the ground isn't going to be able to keep up with even the most basic of usage. It takes a LOT of solar panels, like a trailer roof full, and bright sunny days to effectively recharge this thing.