If you just want to charge your battery, watch telly and nothing more the Honda i10 is enough Ours does a week on a gallon of unleaded that's running maybe 3/4 hrs per night and slipped under back of van with the exhaust sticking out you can't hear it from the front Some sites however do ban them and we only really use ours on sites with no electric when parked next to a hedge
Just checked the price of Efoy comfort 210 couldn,t believe my eyes. Its just under £5000. Can,t see many people being prepared to pay that amount for camping use.