Funny how some guys don't like the single disc brake. I never had any issues with it.
When I got my Jackal it had a warped front single disc. Stopped fine, perfectly adequate, but the shudder pulling at traffic lights pissed me off.
I got a pair of wave blade discs off ebay ($150USD) and a caliper ($300SD off a ducati. Can buy much cheaper if you shop around the wreckers.) and now it stops scary fast!
Awesome braking with twin discs now. The way it should be, though, the "One finger braking" habit under normal circumstances is a bit scary when you REALLY NEED TO STOP QUICK! It's a bit of a transition back to a handfull of brakes in an emergency.

Peter.