The Brompton reminds me of ya grandmother going to the shops.
I saw the price difference, well before I check on part compatibility and pricing on parts.
What clinched it for me is the Mu frame is really graceful with the nice arch throughout the bicycle. I'll compromise on the fold and slightly larger size just on that alone
The Dahon website states the spec as budget to luxury based on the drivetrain mostly, all on the same frame. So with the Dahon, you can buy cheap, and upgrade to your pleasure.
Kinda stuck with hard work on the Brompton to up the spec, and with a larger base price to boot.