the 1950s Cyclemaster, made by several companies (Harding and Rabeneick for example) to compete with the Whizzer, is my guess

so, it seems to be only useful at high speed. That's now when I want an engine to do the work... I want the luxury of NOT pedaling uphill! 

 

was a great look at one, but, the following link has a much faster glance

https://www.facebook.com/groups/1322958884430294/?multi_permalinks=4425731517486333