I've snorkeled in Hawaii and Tahiti so I had the same concern. I have read nothing but positive about the Chileno Bay trip. It is a bit colder than we are used to but I figure why not add it to the cruise/snorkel experience. My DD 7 will be snorkeling with us and my DM will be enjoying the water from the boat. The only concern I have is the water is a little colder that we are used to. Throwing in the wet suit and skins.
Here is one review I've read....
By contrast, Cabo San Lucas was **wonderful**, and anyone even remotely interested should book the Chileno Bay Sail & Snorkel. Ive not had that nice a time on an excursion anywhere else Ive been. Plenty to eat and drink, really friendly helpful crew, and water so beautiful you could see the fish quite well from the boat if you didnt ultimately want to get in the somewhat cold water. There were several little kids who didnt want to go in, and the crew gave them bananas to break up and toss overboard, which made the fish come right up to water level... it was great... and its a lovely stroll to town from the pier... that was definitely our best day.