Some parents at school have a Tern with the continuously variable hub. The bike has been back to the shop twice in the last 12-24 months for issues with the gears. n of 1 sample and all that, but with my wife's e-bike I opted for the 8-speed derailliallier as it's an idiot proof* system that can be fixed aby any shop/me.
*Unless the bike shop what sold it made the chain too short for it to shift properly... But that was some pounds at the LBS and not posting it back to the shop or a 40 mile round trip