This particular winter has been perfect for a heatpump+gas combo. Mostly been between 0 to -15, so it did its thing and ran relatively cheap. Technically we don’t have to think about it, because the way the thermostat we have works is if house can’t hit desired temperature after set amount of time (at or below 2 degrees from target for 45 minutes in our case - this can be adjusted a bit if desired) it kicks over automatically to the gas. Since we saw this almost -40 crap coming we just put it to gas only a couple days ago just to not think about it. I think there are “smarter” thermostats out there, but this has worked fine for us.