We did the morning cruise which is longer (4.5 hours vs. 3 hours) and includes a continental breakfast and cold cut lunch. Pricing is a bit expensive if you are paying full price ($105) but with the Entertainment Book you can save a lot of money with their buy one, get one free coupon! Also, singles are given a 50% discount if you don't have a second person with you. This is a full-service snorkel cruise that includes your gear too.
The snorkel area they use is near the old airport, which is not the best snorkel area around Kona. I prefer the Captain Cook area, or off shore at several of the area beaches. We saw a fair amount of fish and the coral is pretty. It is unfortunate that to really enjoy the coral, you must get pretty close to the shoreline, which has the boat hands whistling you away due to the rough surf. All in all, this is a good value trip for first timers, or those who need a bit more supervision and assistance in their snorkel experience.
They also offer floating noodles and tubes to lounge around in the water if you just wish to lay out and not snorkel. If you do not have the Entertainment Book, look for the $20 off (per couple) coupon in the (Kona) Hawaii This Week magazine. It can be picked up at most hotel and resorts as well as restaurants and other tourist areas.