"very inefficient" and "much more efficient" are probably stating it a bit strongly. From what I've read, both induction and switched reluctance motor types are over 90% efficient, like 91% and 94% efficient. The reason the reluctance motors are used in the M3 is more because they are cheaper than the slightly better efficiency. They are cheaper because they don't need magnets or windings in the rotor, just plain steel. The reason reluctance motors weren't used in the S and X is because they are very hard to get right (require very fast switching), and have a problem at max output called 'ripple torque'.