So what are your opinions about the Brompton parts, they seem pretty old fashioned and has anyone had issues with that flimsy looking derailleur system?
Yes, highly proprietary bike, old fashioned, pastic parts, and not best looking IMO. However it's my bike of choice after using BF NWT, Moulton TSR, and Dahon. Somehow it just works well all around. It also has excellent spare part availability and long term support. You can order spare parts and upgrade kit online by SKU
http://www.sjscycles.co.uk/brompton-shopbrompton_pg1/
If you are test riding a Bromton, make sure to try both M and S handlebars. They provide very different ride experience.