Here is a simulation for a brushless hub motor in a motorcycle. It should give a better representation of efficiency as it relates to speed.
The black line represents efficiency. Notice the bump and subsequent drop as the vehicle approaches top speed. This coincides with the steady state curve I showed earlier. It seems that efficiency is greatest just before top speed in this simulation. It also shows that efficiency is about 20% lower at half of the top speed, and over 40% lower at a quarter speed. All of this supports the need for a multi speed transmission. It also makes me think more that Brammo might not have made a mistake in their design. Maybe the reviewers simply didn't understand the proper use of the transmission as it relates to extending range aka increasing efficiency.