I happen to think they're rubbish & can't imagine why anyone would want one - they do nothing to help congestion, and when you take into account the energy they make (take) to manufacture, you do a better service to the environment by keeping an old car going than making a new one - however it is fuelled. Was what I meant.
Still, each to their own!
A very valid comment. Use the old ones to extinction then buy a new one, it's more environmentally friendly. The motor industry are probably rubbing their hands and saying "Recession, what recession?".