Absolutely worth every $$$ and every minute.
Especially if you have never attended any similar class - I'd say it is near mandatory in order to fully appreciate what the car can do, how well it is engineered, and what you can do in the car in being in control.
The two day class is worth much more than the one day class. The first day's lessons only take full root with repetition on the second day, and you will be very pleased with how much differently you approach the car on the second day. The instructors very much agree with the value of the second day (in any of the schools, actually).
BMW custom helmet is provided on the second day. It is not needed on the first day. It is a very high-quality item, with custom paint.
[Reference - I attended the two-day Performance School a year earlier as a high school graduation present for my son. I was somewhat ambivalent about going through another two days that I felt might be repetitive and not fully useful. WRONG! The M school is much more race and stunt oriented.
Bottom Line -
(always wanted to use one of those ...)