I had a birdy and replaced it with a Brompton. I didn't tire of the Birdy, on the contrary. However once I had the Brompton the Birdy started gathering dust so eventually I sold it. The arguments of a Brompton not having sufficient gearing range is ill informed IMHO. I never had problems and I found it easy to extend my gearing to 10 speed, while I also have a Schlumpf which further increases the range to a huge range unmatched by most derailer systems. Sure it has limitations but the majority of those limitations are in the eye of the beholder.