In the case of you are having a short holiday plan in Phuket, but you are interested to do the double excursions on one day. I very recommend you book the day trip of Yoa Island + Khai Island in one day. The tour can let you do the Canoeing at Yoa Island. There is a Sea Canal from the north along side to the south. Canoeing pass the beautiful green mangrove safari and full with the wide life. In the same time, you can study the living life way of local people on this far a way island.

In the same day and nearby, the trip will stop to do snorkeling on the nicest small Island of Phuket - Khai Island. Just one nice sandy beach surrounding the Island, you are able to do the snorkel from the beach. A million kind of fishes and coral reef under the water can be seen very easy.

PP Island tour: PP Island is the most popular place for snorkeling at the moment, there are so many tour companies provide the day trip fro the tourist from Phuket. The problem of the tourist is that how to consider  to book the better trip with the better company and yes better service.
Some company offers very cheap price, some provider offer very expensive trip and some offer a reasonable price (It looks like). What is the best?

TripAdvisor's review is the one for the tourists around the world like to read before booking. However, the review had been written from the emotion of a tourist. That means we are unable to consider as 100% about the whole standard of any tour provider. 

The good idea is that you have to contact and talk to the real people (Not digital people) and ask them all the detail yourself. If they are a professional about the trip, they will give you all details very KISS.