what is the purpose of eternal bond

[MoonPhaseAlpha]

Big ass diamond ring. That is all

[sarehptar]

You use it and it teleports you to your bond partner's location (or closest island to him if he is flying).
Recast timer of one hour.

Cooldown time is only 30 minutes, and you and your partner's ring does not go on cooldown simultaneously, so you can each teleport to each other once every 30 minutes. While I think 15 minutes would be a better cooldown, it's not quite so impractical as a once-an-hour teleport!

[Culfinrandir]

besides getting the mount and gear and emote what else is there

Exactly the same purpose as marriage in the real world. It's an abstract construct & doesn't actually change anything in reality, just the perception of yourself and others.