Put me in the 50% who believe that it has no redeeming qualities in a modern engine, and that yes, it can harm things.

BMW designed the engine, and the fuel and lubrication systems, and they specifically advise not adding any additives such as these. Maybe they know something about engine design?

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue