Don't know about heat reduction with the privacy glass in the rear. I'm sure it does something. But my tint shoppe guy who's 3M authorized actually recommended that I'd go with Huper Optiks. For heat reduction it makes a huge difference. Only thing is that it's pretty pricey.

I actually read quite a few threads of people praising it also. Check out there website. Pretty cool stuff.

When my X5 gets in, I'm planning on going all around with the lightest (even over the privacy glass). Possibly the sunroof, but still researching more on that (possible glass crack due to immense heat).