It's useful for the commands it gets right, e.g. at night I find the iDrive screen distracting if I don't need the nav feature, so it's easy to just say "switch off display". However a lot of the other commands simply don't register correctly. I've yet to be able to successfully enter a destination for the sat nav using just voice!
2012 F30 328i Lux', 8SAT, Melbourne Red