U brakes as the 2 arms each have their own return spring
I'd presume a little space one way or another could be compensated for by a mechanic with a little flexible creaivity.

In set up : thicker / thinner pads, spacers and all That.

I have a 20" wheel Bike its Made by Bike Friday in Eugene Oregon (only 300, or so, miles from here)

[they have a toll free telephone number to Use in The US]

A travel bike (not a BMX IM too old for those ) I like to sit on the saddle as I ride ..