Why are only a few rentals offered each day?

Because the E-chopper has about 50 km range and so you can tour easily within the rental block (of a few hours) without having to recharge in between. Keep this in mind if you want to rent the E-chopper for a whole day, the range remains 50 km. You might want to charge at the rental location in between before continuing on. Between rental blocks, it is important that the battery is recharged by the rental location for the next rental moment.