On a bigger tank I would think about it, however with a 50litre an ATO is I little OTT IMO. On a bigger tank the water loss would be less of an issue IMO. Might just mod a USB lead with a variable or fixed resistor it reduces the pumps output a little.You need yourself an ATO (Auto Top Off) 😉
I am thinking about the ATO you have for sale, exchange of contracts for new house should be next week so holding off any more purchases ATM