Avis - Driving to Prague, CZ

We're taking a trip to FCO this summer and am thinking of 3-4 days in Prague. The option I'd like to take (for other reasons) is to fly FCO-VIE and rent a car from Avis to PRG. Either that or TXL and drive down via the autobahn. Both ways look pretty innocuous --- not bad at all. Was just wondering if anyone has experience renting in Germany or Austria and driving into the Czech Republic (not one-way so I'm not worried about drop fees) and then back to the same point of pickup to drop off?

We're pretty set on driving (have done thousands of km's in Europe so this is pretty easy) so other modes of transport not really on the table. Avis --> PRG, anyone ever done it?

There may be some geographic limitations where you can take the car. These may vary by country of pickup, and importantly by car class. (Rental agencies don't want S-class Benzes going into high-theft areas, for example.) Check reservation details carefully.

Yes, I'm aware of the car class and geographic limitations. Just wanted to know anyone's personal experience as in how practicaly difficult (or easy, preferably) it was in checking out a specific car at either TXL or VIE for request to be taken in CZ. Do they give you the 3-speed stick, 3-cylinder 4 year old cars with a lot of hassle, or is something like this done often that it's not a big deal?