my Urban Arrow had roller brakes. They were shocking, and i seem to recall there was a warning in the shimano manual that warned that they were only suitable for bikes of something like 100kg including the rider, which didnt leave much slack on a normal bike, let alone a 50kg-dry cargo bike.
I think they are legally on thin ice speccing them at all.
It was ok, as long as you planned your slowing well in advance, and didnt take routes that involved hills, but i had a few ruddy sketchy moments where stamping on the brakes as hard as i could wasnt doing enough to stop me just rolling into the back of a car, so decided to get some disk brake tabs welded on the fork.
problem then was, with no load in the front it didnt have much grip so it was very easy to lock the slick front wheel into a slide.
Solved that by getting a super tacky BMX knobbly (Schwalbe jumping jack).
Then i sold it.
Doh.