Folding bike enthusiast here, since 2005. I always thought that buying a Brompton would be a dumb decision: the bike is not that good looking and as a (unfolded) bike had pathetic performance.
I tried pretty much everything else, from Giant Halfways (including the rare asian one with rear suspension), several different models of Downtube, Dahons, Bike Friday and a Merc. Once I got the Merc, I started to uhange my opinion.
Saved the money, got my first Brompton in 2008, never looked back. Best folding bike ever (for my needs).