Recent Road & Track article about the different type of start/stop technology/systems. Included some subjective ratings by the editors and IIRC, they gave BMW's either last and next to last as far as being seamless and working well. They basically said the BMW system is the least technologically advanced and not well integrated.
2009 335i Coupe/DinanS3/Dinan CAI/Dinan High Capacity Oil Cooler/Dinan Intercooler/BMW PE/M-Aero Front/M3 Rear Spoiler
2006 Z4 3.0si/AA Tune/RPI Intake/OZ Ultraleggera/UUC SSK&DSSR/Cosmos Racing Strut Brace