The first time I dived there almost 20 years ago, it was on air, as were my buddies, none of us had Nitrox cert as I recall, and nitrox wasn't quite as ubiquitous as it is nowadays.
It was okay, as during that first year, gas was my limiting factor rather than nitrogen load. And my hockey puck computer was not nitrox compatible anyhow. And I kept it less than 100' which I recall was the boat's rule.
Then I got Nitrox cert, and computer, about a year in (with not all that many dives, maybe 25 or so). By then I needed it, as my gas consumption had improved, and Nitrogen loading was beginning to be my limiting factor.
Nowadays "air is rare", and Nitrox is common. I use air only on the shallow venues. Also it can be a bit awkward if you don't have Nitrox and buddy does, or vice-versa.
Enjoy the Flower Gardens! A beautiful venue, and the operators are good. If you're lucky enough to get a platform dive and/or a Stetson Bank dive, that's the trifecta.
PS: listen to Wookie, he was the Captain, and later the owner as well, for most all of my FGB/Stetson trips.