My wife and I just bought a Brompton and Birdy. I'm new to folders, and this site and thread have been useful. Here's some biographical info for other newb's. If it fits, wear it. Obviously, your mileage may vary.
I'm in NYC 2 yrs. Ready for a bike. Folders? Who knew? Holy whoop! These things cost $7-800. At least the ones that aren't the cheaper ones. OK. I can do that. But some cost more. What's the diff? What are the decision-making rules?
Well, I may be new to folders, but I'm not new to . . .cars, guitars, espresso machines, cameras, to mention just a few lifelong passions. Is there anything transferable about buying these other "products" and buying folding bikes, about which I know nothing?
1. Bang for the buck. Here, the point of focus seemed to be the Dahon MU XL Sport. Originally around $1100, but getting dropped from the Dahon line, and couple of shops offering it for around $850. A fine ride, reasonably compact when folded, within a pound or two of anything not titanium. There's really nothing about more expensive bikes that is "that much" better to justify a cost factor of 2 or 3x. And yet . . .
2. "It's the delta" Years ago I had a contractor doing some remodeling. His mantra was, "it's the delta"----or, what's difference between what you must have and what you really want. "You gotta have a toilet. So subtract the cheapest toilet you can live with from the cost of the toilet you really want." That's the delta. That's the actual cost.
So I bought the Birdy. The delta was about $1200, and I got finish, quality upgrades, extra (if marginal) performance, status (the coolness factor,) long-term satisfaction before GAS (Gear Acquisition Syndrome.) My wife's Brompton choice followed a similar process, but different factors.
This isn't a recommendation for a bike, but a process.