💏Billings Ovulation Method - Advice Please?💥✨🌟

Ma
Hey! 
So, who among you use/has used the Billings Ovulation Method? 
If so, has it worked well for you?
What do you understand the "peak" to mean? 
Do/did you have sex without protection after your "peak" (and the necessary 3 days of protection/abstinence afterwards)?
If I were to use the BOM with Glow, how would I calculate my 'peak' and start counting the necessary days until I could have PIV-to-the-finish sex without a condom? With the peak being the day I have a 30% chance of becoming pregnant? (Especially since Glow sets two highly fertile days after that peak).
Thanks for any and all advice! Ask for clarification if needed, please :)