I did an experiment. I have avoided the feature like the plaque after experiencing it just once. So I put it on and insisted not turning it off until I reached my destination.
It turns off quite cleanly, not startling. I find it's much better with the manual since if I anticipate the light will change soon or some other instance where I want to intervene, I just press in the clutch to block the engine from shutting off.
However. Due to so much vibration from the shift lever(mainly an N20 issue) and the fact that I am always at the ready with my hand placed just so, the re-start is startlingly violent. If BMW can improve on that one aspect(also all the mounts may further break in which would transmit less vibration) I think in the manual at least it would be successful and I would use it more often.
'98 Dinan/RMS stage 2+(VAC cams, CES Cutring etc)
'15 Buick Regal "T"(wife)
'06 Saab 9-5 Combi 5mt (full suspension, LSD, clipped turbo etc)