Koh Kai consists of 3 smaller islands: Khai Nok, Khai Nai and Khai Nui. Koh Khai Nai is the biggest (see top) and it's also the home of many cats with numbers (vaccines). There are also small restaurants and ice cream shops. Koh Khai Nok (see previous) is smaller but is the most beautiful. There's also a small restaurant and bar there. Koh Khai Nuai (see bottom), doesn't have a sandy beach, but it's great for snorkeling. The 3 islands are clearly paradise postcards and you can launch drone. From koh Khai nok, you can even launch the drone to koh khai nuai, as it'snearby. It's also a good spot to use an underwater dome.

Usually the tour takes 4 hours, so you stay 45 minutes per island, so use your time wisely. If you rent a privtae boat, that's much more expensive (I think more than 3-4000 THB), but that would be ideal to spend as long as you want in each island.