Overall great services!
One small issue related with the payment method. Although in term and conditions Sixt states that prepayed cards are not accepted, i’ve made the online payment with a prepayed card. And it worked. This made me think that it will work also at the counter (deposit). It didn’t. So I had to change entire payment (booking+deposit) to a debit card. My prepaid card was issued by Revolut. My suggestions is to ask the costumer services before the payment.