Even though this is a forum for prius but would share my experience on running 0W20 on vezel which is the recommended oil for the car as per manufacture manual. I have been using Honda (total) synthetic 5w30 for 10,000 km (2 oil changes) and then switched to Liqi moly 5w40 for 10,000km (2 oil change). Recently 0w20SN has been introduced by honda (total) for civic turbo so i decided why not. Following were my observations after using the oil for 500km till now,
1) Car feels more light on the pedal (same as you would feel from super to hi-octane)
2) The transition from hybrid to engine and vice versa is more smooth (previously i could feel a bit of jerk especially when i started to use 5w40 liqimoly). This observation is vezel specific. Not sure how toyota hybrids would do.
3) Fuel economy , its a highly debatable subject and would vary from user experience. But can say 0,5 to 1 km/ltr additional.
4) Since its winter now (atleast in isb in the morning) cold start and warm up is fast, makes sense (low viscosity oil comparing to 5w30 or 5w40)
I am no oil expert here just sharing my experience.