Two swim aids that don’t look dissimilar but have big differences in the water are hand and finger paddles.
Finger paddles are the smaller accessory of the two. The paddle covers the surface area of your fingers and allow you to work on the top of the stroke, specifically hand entry and catch, which is the action of pulling onto the stroke. Finger paddles are great for technical swimming and are especially useful for technique drills if you wanted to break your stroke down even more. If you’ve never used finger paddles it can take a few minutes to get used to them, however this could be due to them showing flaws in your stroke, and can make you feel a bit unbalanced in the water.
Hand paddles are much bigger, with the surface area covering beyond the tops of your fingers, down to the bottom of your hands. This allows you to hold to much more water, with more power and leverage to pull through the water. These can also assist with balance in the water whilst also allowing you to spend more time on each specific pull, making sure that you can really working on finishing your stroke, which in turn should lower your stroke count.
Both paddles have their physical benefits, hand paddles specifically are great for longer distance sets and can make a tougher work out due to them recruiting more muscle groups, increasing strength. Gains can come in any form and both of these aids could be really helpful in securing vital seconds in your next race.