I bought and installed the clutch band brake kit from OldMiniBikes and all I can say is WOW! I wish I had done that a year ago when I built my bike.
I have been wary of the rear brake because it never really had much stopping power, but the clutch brake stops on a dime.
I left the rear brake on and added a brake lever on the right handle bar as a backup in case my chain breaks or comes off the sprocket.
If you are wondering whether to add a clutch brake or not, just order the kit and do not look back.