Yes, a 3 speed will offer some advantage over a single speed. How far you are riding, how strong a rider you are, and what the terrain looks like will all affect how much benefit you'll see from 3 speeds instead of just one but there is almost sure to be some benefit.

If you want a multi-speed freewheeling bike just get the Oxford which comes with a freewheeling 3 speed. this bike also has fenders and bigger tires which would be nice for commuting.

-Or-

The WT5 which has a freewheeling 5 speed IGH.

Getting the 3-speed fixed hub to put a freewheel on it is buying an airplane to get free peanuts. It'll work but there are more efficient ways to accomplish the same goal.