Since long before I even got certified (doing Discover), I have heard all these amazing things about Nitrox. It’s the most popular PADI specialty. It seems like everyone uses it. I finally signed up for the class and doing my preparation and knowledge reviews, I realized that Nitrox has a major problem similar to air - too much oxygen causes problems, just as too much nitrogen does. So staying deep for a long time makes it likely that you’ll push your nitrogen limits, but going to a certain depth with a higher amount of oxygen means you have to worry about oxygen toxicity now. So suddenly Nitrox isn’t useful for deep dives, when I thought that was the entire purpose of it!