So I have the Enviolo (aka NuVinci) IGH. It is a CVT, which means you lose from 4 to 10 percent. It is also significantly heavier than a 1x12 drive chain. However...
1. Perfect chainline like any SS, chains last longer as do sprocket/chain ring - YMMV
2. The Enviolo Electrique sets the near infinite gear ratio to exactly the cadence you set it to. So if you tell it to give you a 70 or 80, or 90... it will go up or down to maintain that cadence at the speed you are going. Pedal faster and it upshifts and you go faster. Pedal slower it downshifts.

So you get efficiencies from always being at the right cadence or close to it. I can change the cadence while riding, making it easier or harder to pedal, depending on conditions. Handy if riding with a group and you want to go faster but not spin like crazy. All in all it is slightly less average distance out of a battery, say 5%? Hard to pin down because how much I can contribute changes, so the distance changes.

Mine is a 40:20 ratio, so I get from 40:10 to 40:40 with the 380% gear spread. For me that means 5 mph up a climb and a top speed of about 36 assuming I don't go lower than 60 and more than 120 cadence. a 2:1 ratio is the lowest they recommend

Bike is powered by a CYC Photon, I rarely use more than 300 to 500w, although it will put out 1500w and the Enviolo HD will handle it plus me pedaling