I've ridden in a Prius before; although it does have a very smooth transfer from electric to gas, and when "adding" electric power to gas, it still has a slight shudder sometimes.

I've never ridden in in any vehicle equiped with an IMA system, but I do know that it is a very simple, elegant system compared to HSD. Honda rules.

But does Honda, renowned for highly refined engines, have a highly refined IMA system in the HCH II ? Does it shudder comming out of auto-stop, and can you detect when the electric motor is assisting? Is IMA more refined, less noticable, than the current HSD?

It is very smooth going from auto stop to start. If you drive normal you will get a very smooth transission. Once you learn the instruments, you will know the mod you are in, at a glance. Regen, assist ,EV mode and stat of charge of IMA. H