Just to be clear, the "clown bike" comment (and I said "more like a clown bike", implying a bit of clownishness in the Swift as well - they both have twitchy/agile steering), apart from being a tiny jab at the Brompton's looks (tiny because I'm much more interested in performance than looks), was about how it is to ride, in comparison to a full-sized bike.

Don't get me wrong, I'm still very impressed with the Bromptons, and they're what got me looking at folding bikes in the first place.

But when I test rode the Brompton, I could feel flex in the frame, I could hear the joints faintly squeaking, the shifting was more fiddly and less crisp (and I was aware that those parts would be comparatively difficult to swap out). The impression was "this rides surprisingly well for a bike that folds so small", where by contrast, my impression riding the Swift was an unqualified "this is a really nice-riding bike - are you sure it folds, too?".

Add in that the Swift was in the ballpark of 2/3rds the price of a Brompton, and I came to the realization that, though I was quite taken with the Brompton from an engineering standpoint, the Swift simply rode better, and folded enough for my purposes.

Getting back to the original question, it's very hard to engineer out that last couple percent of flex from a folding frame, and the Swift's solution is ingenious, in that the only hinge uses the seatpost as the pin to secure it in place, making it extremely rigid. Everything I've read about the Bike Fridays suggests that they're superbly designed/crafted bikes, but I'm still left to wonder how well they've conquered that last couple percent. That, coupled with the substantially lower price of the Swift, is why I was quite happy with getting the Swift without having riddden a Bike Friday yet.