A drum brake? On something like this? I hope it's not a drum.
I'd not be too bothered myself. The back brake on a three wheeler does not want to be too good. Admittedly with a far narrower tyre, but having locked the back on mine at less than 30mph, it is a brown trouser moment. Whilst an excess of power is controllable, a rear wheel skid is uncontrollable on one of these.
The braking effort distribution could easily be 80% front, 20% rear on this design.
Provided the arrangement can cope with the heat produced, no problem.
