I've been using folders for years, as they were excellent for folding and putting in the camper. I've had 3, and all ended up getting stolen, two in Holland, and one in Ireland. They are truly excellent bit's of kit, and they do offer a similar experience to a regular bike.
I have however, after reading many reviews, and a lot of heart searching, replaced the Bromptom with a John Whyte designed Mezzo D9. It is similarly priced to a Brompton, around £700, but for me, it's a much better ride. Why?? The ALUMINIUM frame doesn't fold, so it's much more rigid. It has a much better component fit too, Shimano Tiagra/SRAM mix, all really good quality. Unlike the Brompton, where all the components are Brompton specific, all the Mezzo parts are easily available from your local shop, and this also allows you to upgrade to whatever level you wish. It does fold up to a package about the same size as a Brompton, though the experts say it takes about 5 seconds longer. My god, a whole 5 seconds!!!
The biggest bonus however, is that it's not a Brompton, and because it is less well known, is less attarctive to thieves.