Ask to join the CharterBoatOwners group on Yahoo, then ask a lot of questions about the good, bad and ugly, to make sure you go into it with your eyes clearly open. Some owners come away with great experiences, others not so much.
How often would you use it and for how many days? There's a break-even point at which chartering makes more sense. Generally speaking, if you can't take sailing vacations at least 3 times/year for a week or more, I would suggest staying with chartering. However, if you want to sail there a lot, then it can be more advantageous financially to own. But when I say "financially", I just mean the cost of sailing in paradise. It's not a good investment in the sense of getting a return. Your "return" is sailing time vs. cost.
One advantage of TMM and Horizon is you can use boats in their fleets in other islands (I think, but not certain).
We did what you're considering in 2012. If you want to send me a PM, I can give you more background.
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