Effective is a client-side Quilt mod (older versions being on Fabric) that adds various visual and auditory effects lacking in Vanilla Minecraft to improve overall ambience and feel of the game. Currently, it adds water and lava splashes to entities falling in liquids, as well as cascade visual and sound effects.
https://www.curseforge.com/minecraft/mc-mods/effective
Yes: You can. Go ahead, don't bother asking. Please however provide credit and a link to either the GitHub repository or Curse Forge project page.
Yes: If you have installed this mod on your Minecraft client, you will be able to connect to vanilla Minecraft servers and the ambient effects will work as intended.