Heavy metal music is not suitable for any yoga class, even some “burn” class. After all, yoga is meditative practice while it benefits one’s physical. Good Zen and/or Kundalini music can better inspire both mental and physical strength. Yoga studio is like a temple in the sense, not a gym.
It is odd or not quite appropriate that some instructors use notes when teaching, it makes the class lack of flow and shows that the class is not very well thought out or prepared.