Agressive EOC and engine off at lights gave me massive gains on my MB100, over 15%.
BMW and Ford have auto stop start systems and quote
3 and 5 seconds as the break even period. I have auto stop start on my Fiat
I won't buy another new car without it.
Most people will agree that starting a hot engine takes very little power and places minimal stress on the starting system, though it may be a good idea to add a solar panel to keep the battery fresh (which is what I did).
I bump started where possible though.