It's a one-size-fits-all design and if it's a little off you're kinda out of luck. They fit me perfectly though which is one of the things that blew my mind initially. I didn't realize how many of previous fit issues were a result of having a cord that tugs when you make any movements.
* like pretty much all Apple earbuds, they don't seal to my ear so they're totally useless in loud places like airplanes (my #1 use case for headphones)
* audio frequently drops out, especially when outside (and there's nothing for the bluetooth signal to reflect off of)
* terrible mic quality for phone calls
* unreliable pairing to my Surface Pro
* one more thing for me to forget to charge
Some of this is anecdata and maybe I just have lemon AirPods, but my experience has been very far from "there's no going back and there's no comparison". I'd sell them without reservation if I didn't feel weird in general about selling earbuds.
A couple of those points are not my experience at all. My audio never drops out unless I'm far out of range or in a weird weather environment and my mic quality is excellent (in fact, I take calls regularly).
It's so drastically better than anything on the market, that I'll immediately buy a new pair if I lose my current ones. I wouldn't even think twice about the price.
There is no other headphones on the market where I can play 1:1 basketball for hours, have the headphones never fall out, and I don't even notice I have them on the entire time. They're a part of me. I literally forget that I have them in my ears, and they easily switch between all of the devices in my life in a way no other headphones do. It's a signficant quality of life improvement for me.