I was stung by a jellyfish on the 1st swim and had a really bad reaction. Luckily, the scenery was so amazing and the group was so awesome that it didn't put too much of a damper on my fun at all. During the week, 2 other group members were also stung, so just something to be aware of if you have a major fear of jellyfish.
That said, the swimming locations were just plain magical; everyday I just couldn't believe the beauty I was surrounded by. I did this trip as a casual swimmer who only lap swims occasionally and while it was tough, it was doable. I never felt in danger and always felt well looked after by the guides.
The kit list should be updated to recommend aqua shoes and insect repellent; both are really necessary. I wondered if hiking sandals would be appropriate for the hikes and I can say now that I am glad I brought regular trail runners in the end. Another thing I will mention for future travelers, I assumed there would be places to change at the beach after the swims, and that was generally not the case. We usually ended up changing under a towel, so it would be good to bring something to change under like a changing robe. I think other reviews mentioned the very late lunches, so definitely plan to bring snacks to eat between the swims and the hikes. Breakfast was usually at 8am and lunch was around 3pm, so it's a long time with just small bites of fruit or biscuits if you don't bring anything for yourself.
The group dynamic was great and everyone was so supportive to each other. I highly recommend this trip if you're solo. I think only 2 people on this trip knew each other and the rest of us were solo and we had a good age range where no one felt too young or old to get along with everyone else.