No, I've never used them. But could the campaigns I play in withstand their introduction? Of course they could! The one thing I might do is change the name to help discard the baggage associated with them for players who get distracted by the notion. Perhaps I might called them wheeled horses, or town-horses (since they're best on paved surfaces). It might cause some comment at first, but by comparison with other things I have included (magical concrete, moving roads, flying ships, etc) it's pretty mild.