This cannot be understated. They smell really bad. Have a friend who lived in Prague and his bathroom wasn't ventilated and he had a german shelf-toilet. Day after a big drinking session, it was unusable since the room smelt so bad.
Double plus for no splashback. I don't get how people can suffer through this. I hate so much being splashed by dirty toilet water. And this happens like 50% of times for me while using non-german style toilet.