suggest you post to folding bike forums...it is very active with extremely knowledgeable enthusiast riders.
IMO Brompton is a great choice....but do not rule out Bike Friday Tikit. Also very durable, with front and rear load carriers. Not quite as small as Brompton but folds fast, rolls folded very well on front tire with a handle and and is easy to carry with a handle. It emulates the riding position and wheel base of a regular bicycle and is generally fast bike. (I own one).