A good coaster brake will allow you to skid the back wheel so in that, it stops as well as a fixed gear (sans brakes) and whenever possible, I have retrofitted many coaster equipped bikes with an additional front brake to improve the braking.

Coaster brakes were not designed for high speed use or long descents as they generate a great deal of heat and have a tendency to fade when they get hot.



This is my 1940 road / path racer and it was equipped with a front brake after I was unable to prevent myself from broadsiding a car that pulled out in front of me... the brake was working as well as a coaster could and know that if I had a front brake I would not have hit the car.

It is too fast a bike to only have a coaster brake and is exceptionally fast on descents... a coaster brake would get so hot on these that it would burn your fingers and probably stop working.

I know this from experience.