Disc brakes are great breaks that has the power to stop the bike or car with better braking systems. And for city driving disc brakes would do better only.
I have had three vehicles with rear disks. I am telling you, they are great and you can stop better than the Disk/Drum setup. Never a problem with them.
Its really safe to have one in rear side. But make sure that you are a good driver and you have a good control of it. Its really drangerous to have disc brakes in the front. And more over the vehicle should be of more weight to have better control.
Disk brakes itself is not safe for normal drivers, It will lead to skid at any time once we apply it suddenly. So try avoiding use of disc brakes on your drive