New Smart are made by Renault, you can look at the Renault Twingo, they share a lot of the interior and powertrain (sadly for the interior...).
On my gf's Smart, engine was quieter with Petronas Syntium 7000 0w40 oil (I think Petronas is one of Mercedes suppliers), which is a thin 40, but it's not readily available in the US, lol
Granted, not same engine but same series from Mitsubishi on yours (?), I'd rather use a w30 oil with 229.5. Or Castrol 0w40. As arbitrary as it sounds, her engine sounded best with Castrol than M1 or the current SHU.