Heat pump experiences - assessment?

Yep - you always have to adjust a heater yourself. But that was already true for fossil fuels.

... constantly accelerating and coasting in low gear with the combustion engine vehicle ...

is actually the most efficient way to move a combustion engine. That’s how fuel-saving competitions are run. The reason lies in the power curve of combustion engines: the sweet spot is at almost full load and about 2/3 of the nominal speed. So, a bit different than with heat pumps. ;-)

Interesting. What does full load - full throttle mean? And what is the rated speed or where can I find it?

Performance charts for many engines can be found on the internet. There you can read torque, speed, and power. From this, one (or more) optimal operating points can be determined. It is important to note that the power must actually be needed. It’s no use driving at the optimal speed if you don’t need the theoretical power at all. In that case, less throttle would be more sensible. Or as we mentioned above, take your foot off the gas completely and coast.

The issue of required power is the reason why combustion engines have an efficiency of around 10-15% in real operation. The theoretical 35% efficiency is reached exactly for 10 seconds when entering the highway. For the remaining 99% of the time, every car is overpowered and is wasting fuel or running inefficiently.

By the way, that’s why Toyota developed the Prius: a hybrid without a plug that was still more economical than any other combustion engine. Because it shifts the operating point upwards during inefficient slow driving. That is, it loads the engine more and charges the battery with the excess energy. Shortly afterward, the engine can then be turned off completely, which is the optimal state when it comes to saving fuel.

So. Sorry for the off-topic. And if I have explained anything badly, please feel free to correct me – I’m not an expert and I don’t like driving cars. ;-)