Yes, the auto setting will always be inefficient, because it is about comfort and not efficiency.It`s not necessary, but it will improve range in winter significantly. The point of a heat pump is not heating the car fast but using less energy. At auto setting the climate-consumption in winter in the TM3 is terrible. If you set it to manual and run fans at for instance 2 x vs windows and turn off AC when not needed it`s much better. Did some tests and compared with the kia Soul with heat pump and at 0C running climate at 19C the Kia Soul uses about 5% more energy with climate on vs off. The TM3 on auto uses around 15% more on long trips, with the manual settings extra consumption is only 5-10%. In city driving I have seen consumption up to 40% higher at auto vs 10-20% with the manual setting in my TM3. That requires a lot more charging in the winter for my part so a heat pump would be most welcome in my opinion
If you use heated seats and use manual, or set the auto temperature a bit lower, then it's A LOT better than auto.
AFAIK the existing system is very efficient, and clever, as it uses the existing parts to heat up the car.
Set on auto it's kinda like "screw everything, I want to be comfortable NOW!" (which is how I do it ), if you tune it a bit then it's probably not gonna be a big difference with the heat pump. Just based on the law of energy conservation and how the systems work the biggest difference is the speed at which it is delivering the heat and the heat dissipation.
That said, I heard someone mention that the TM3 heat pump has been measured to be efficient all the way to -20 degrees, and in that case I'm probably going to have to eat my own words.