One decision that faces anyone snorkeling in Key West is whether to rent or buy their snorkeling equipment. There are a few factors that go into this decision. Price, convenience, practicality and proper sizing should all be part of the equation, as should the frequency of use. A first time snorkeler may not want to buy gear before they know if they will be using it again. However, a frequent or even occasional snorkeler may find it worth the investment.
Proper equipment fit is very important when snorkeling. If goggles don't have a good seal or are too large, water will leak in and require constant adjusting and cleaning. Frequent fogging is another mark of ill fitting goggles. Conversely, goggles that are too small may be uncomfortable or leave unattractive marks on a swimmer's face. The mouthpiece of the snorkel itself should definitely be the right size to avoid muscle strain or discomfort, and fins should also fit well in order to facilitate swimming and maneuvering in the water. As there are many different types of fins it is also convenient for a snorkeler to be able to own their preferred style rather than compromising on what is available to rent. Anyone who is unusually small or unusually large may face difficulty in even finding rental gear that fits at all.
Then there is price. While buying is obviously more expensive than renting in the short term, in the long term savings can add up quickly. While prices can vary greatly, a good mask can be bought for as little as $50, and a snorkel for even less than that. A good pair of fins may cost closer to $100. All told, an entire set of well reviewed, respectable scuba gear can be purchased for less than $200, which is a higher cost than just a few days of renting but starts to pay for itself after the first couple weeks.
Of course, convenience is another factor. One one hand, it is convenient to be able to head right out from a home or hotel and go snorkeling, without first having to pass by a shop and arrange a rental. On the other hand, for people who prefer to pack light, not having to carry several pieces of bulky equipment across the country may actually be preferrable. This particular consideration can really break in either direction, and depends on each diver's personal circumstances and preferences.
In the end, whether a snorkeler decides to rent or buy will likely depend on how serious they are about snorkeling. Anyone who is snorkeling for the first time and who has no plans to do so again doesn't really need to buy. Rental equipment is very affordable and will likely work well enough for a short first trip out. However, once divers find themselves eagerly heading out for the fourth or fifth time to explore new areas of ocean, it may be time to invest in a good set of equipment. Exactly when that turning point happens is really up to the individual.