Got to the second chart in this article
https://bicycles.stackexchange.com/q...to-derailleurs and look at the efficiency for the Nuvinci hub and you will realize why the company never mentions efficiency in any of their literature.
I rode many thousands of miles on a trike equipped with an older version of the SRAM dual-drive 3X8 and a Schlumpf Mountain Drive. The drivetrain was configured with a 65 tooth chainring and 20" drive wheel. That allowed nearly all riding using the high range on the SMD and middle range for the SRAM dd so that both were in direct drive maximizing the efficiency. If I changed out of either "direct drive" modes and engaged the planetary gears I could sense the loss of efficiency. My current trike uses standard gearing and I bought it that way because of the efficiency and universal availability of repair parts. Try finding repair parts for an internal hub.