I found it a very good experience. Lovely car (upgrade), everything very efficient. I actually booked a car with Flizzr, which I understand is linked to Sixt, but couldn't see any sign for Flizzr in Saalfeld. Luckily Rentalcars had told me of the link to Sixt but it might confuse some people trying to find the office. Also I think it would be good if car hire firms told renters when the car has "lane assist" steering as this can come as quite a surprise if you're not used to it!