I think our HV mode is better than the Prius since on the highway, our ICE doesn’t have to run all the time.
If you want to avoid the buzzing angry bees and always have plenty of power for hills, all you have to do is not let the HV battery completely deplete down to 0 EV range and 2 bars.
For level roads, moderate acceleration, and normal speeds you can get by with using up all your charge and letting the car automatically switch to HV.
But on the highway, and especially with hills and higher speeds, the car likes more than the 2 bars to be able to cycle through all of its possible power flows to be able to deliver the most efficient, quiet, and required power.
On a recent 500 mile round trip with both Interstate at 70mph and hilly 2 and 4 lane very hilly roads at 60-70mph I started in HV with a nearly a full charge. I watched the powerflow cycle though battery only, battery plus generator, regen, generator charging battery, engine direct to wheels, all seemlessly done as far as felt power and drivability. I got 49 mpg and lost only one bar of EV so the mpg was not inflated by using charge. Some times I would see the charge/EV decrease by as much as ~3 bars/15m but then gain it back as the computer decided when use the battery and when to recharge it. Also I have an hour meter and calculated the ICE ran about 2/3s of the trip and cycled on and off repeatedly and rather frequently.
Best of all, I never heard the buzzing angry bees! Before this trip, I had to slow or stop the car and turn off the AC to be able to hear the ICE idling and only once on my first fairly level Interstate trip did I hear it make kind of a fast idle in HV. On this trip at the end of a very long, steep hill, the ICE did rev up to a low to medium hum but not the buzzing angry bees. But at no time did I ever experience a loss of power.
So bottom line, you need some charge in the “bank” for the algorithm to be able to use all it’s possible powerflows in the most efficient and quiet manner. I would suggest switching to HV on highways before you run out of charge, say around 1/3 to 1/2 unless you know you’ve got mountains ahead and then I’d want a full charge by switching early. When you run down to 2 bars ans 0 EV, you can run into situations where the car is limited in what powerflows it can chose and you’re more likely to get the angry bees and driveability issues.
And the only use for HV Charge I can see would be if you are on a highway and approaching mountains with not enough charge.
This is the best car on the road and I want to end the angry bees for all.