So here's a thing. Do you go to a yoga class and see your teacher with bits of paper and open books in front of them? How does that makes you feel?
Having completed my YTT200 yoga teacher qualification I do the same. I take time to research my classes and write up lesson plans, I refer to respected books, teaching materials and publications to keep me focussed on the theme. I familiarise myself with my students health and safety forms to ensure I include posture variations and modifications where appropriate. I keep the lesson plan in front of me when I am teaching and revise it at the end of each class if something needs to be tweaked.
Most importantly by following this methodology I know that I am delivering a class that has my students wellbeing and safety at the heart of my teaching.
If you see a teacher with the same handwritten notes, lesson plans and books in their classes then be assured that they are taking their role as your yoga teacher very seriously.