A few minutes during a test drive is not enough to understand the pros and cons of B and D.
Once you have the car, I suggest that you try again over an extended period.
That's what my wife and I did when we got our Golf GTE nearly four years ago.
I enjoyed learning the technique of using B properly and have continued to use it exclusively ever since. A little adjustment was needed when changing to the November 2020 ID3 but 2.1 upgrade takes me back to virtually the GTE technique.
My wife has stuck with D after her experiments. That means our brakes do not rust like they would if I was the only driver.
It's a very relaxing car to drive either way and I doubt that you could measure any difference in economy.
I'll have another play when I get the car, but for me, I'm pretty sure I'd rather drive a car that's wanting to keep moving rather than trying to stop without your input. It's more economical to preserve your momentum and minimise waste rather than rely on a recovery system that is probably 60-70% efficient.
I'm presuming that using the brake pedal to a certain extent activates the regen rather than actually using the brakes and the actual brakes kick in under a firmer pedal press, as they would in B mode anyway - is that correct? If so, I'd think that driving in a way that generally preserves momentum in D mode would be noticeably more efficient than driving in an uneconomical manner and rely on "B" mode to save you some of that wastage.
I used to smash the combined mpg figures before stop-start massively skewed the figures. Even now, my missus averages 33mpg in our Polo GTI+ and I average 37mpg doing similar journeys. I get up to speed quicker than her but brake half as much as she does...anticipation of the road ahead.
