I`ve only ever used one of these toilets once. Travelling by coach through France to Spain, in 1984, the toilet on the coach was faulty, so we stopped at a rest area at the side of the motorway. There was a queue a mile long, and everyone returning was chuckling, but wouldn`t tell us why. We soon found out! To be fair, it was reasonably clean and not too smelly, but I wouldn`t like to make a habit of it.
The nicest public toilet I`ve ever used was at Ephesus in Turkey. They were partly underground, spotlessly clean, and smelt of lemons, with the most delicious smelling lemon soap.