CVT are really lousy on anything having to do with bicycles. CVT are fine on go-karts and motor scooters, but good luck trying to ever pedal anything with a CVT.
Might as well not even have a bicycle at all with what that drivetrain offers.
IMHO, the best bang for buck 4-stroke is a 4G kit with Huasheng or a Q-Matic kit with a Harbor Freight motor.
If you want to have shifting capability, then a B-E 4G kit
with SBP shift kit
is the way to go.