We did it on Celebrity last May. It was a mistake booking thru X. Why? Because your stuck with a huge group, and the pace can be really slow. I told myself that if we ever go back, I'd show up on my own and pay at the entrance. They give you head phones and you can do the entire excursion on your own. I highly recommend this! You'll be able to go a lot faster and do other things the rest of the day. Trust me on this, we had a really, really slow group and guide!