To understand:

You can do in this mod:

• start from water and toggle elytra-flying mode
• toggle elytras in waters, to not having going on land either

Landing in water

• means you natrually need to unequip your elytra, but when doing so, you need to go to solid ground to restart flying, right?

• with this mod, you can simply take off in the water again, you don't need to unequip the elytra anymore

• and being in water means, you can press Space to toggle flying in the water, which also means you can go swimming or fly

• (there is also the Gamerule: "elytraNeedSwimToFly", which means if you are swimming - sprinting in water - you HAVE TO SWIM to start the elytra-flying, like already being in the crawl pose), this is usually set to FALSE

these only work above over the ocean inwaters, not lower in the ocean (will be fixed somehow)