I have them and have used them every time I have taken my new M3W out for a ride....it should be noted that I took delivery of my car on December 23rd, and I live in Connecticut! All cold weather rides thus far!
The heated seats do get rather warm....almost on the verge of being "hot". I have to switch them off after a while, and toggle them on and off on longer rides in cold weather.
For the relatively low cost of the option, I recommend them.
