It was a great day when swim fin booties were invented! Unlike the smaller version fin socks, which use less material and are geared more toward aiding uncomfortable fins, fin booties cover the whole foot and keep your feet very warm in cold water so your feet don't freeze.
Booties help individuals conquer waves and water that was previously inaccessible to surf for long periods of time, especially in Central and Northern California, and the U.S. East Coast. These locations have incredible surf but very low ocean water temperatures.
By wearing swim fin booties, your feet stay toasty warm and you can ride the waves as good as in the summer time in warm water.
They are made neoprene or wetsuit material. The usual characteristics of this material are soft, cushiony, stretchy, and water resistant. The material is sown together at the joints and the premium booties have a rubber strip over where the joints were sown (just like a wetsuit). This keeps the joints water resistant for a longer period of time.
Over time the seams will eventually loosen/tear and water will seem in. The rubber molding on higher end booties will last this for a longer period of time and for a small price over the standard stitching, it is a great option.
With most products, you get what you pay for. When your shopping for a pair, the higher the price the better quality. Rubber seals are better when compared to stitching. Neoprene material have several grades and the best booties have very stretchy and durable neoprene.
The rubber footing on the soles should only be used if your are surfing with a shortboard or longboard. It is great for surfing while standing up on your board but if you are a bodyboarder, swimmer, or bodysurfer it will take away from your maneuverability and flexibility.