[Pete]

As with anything, it is the overall combination that makes or breaks success.
With zephyr gears the engine has a lot to do with success. You need an engine that has a lot of torque just off idle and yet will turn to a reasonably high rpm.
Most people try to run too high rear end gears which hurts around town driving.
For a good all around combination with zephyr gears you need an overdrive or a 4 or 5 speed transmission.
Back when these gears were popular, a very good combination was the 4.44 rear gears in a Columbia axle. This was a stock setup in the Lincoln's, however, most people got a set of Getz gears for the Ford rear ends because the Lincoln was a hypoid type and were quite a bit heavier and bulkier than the Ford.
The zephyr's can be made to work very well and they are harder to break because of the lower torque multiplication. You still don't have the convenience of all gear synchro as with modern transmissions though.