Using the HPBonus you can give it a description which will show up in the character interface as a HP bonus but it wont show it as a buff.What's the advantage of using the buff system instead?
Say you want to have more things which buff davy jones you can group them or only take the HP bonus and add them to a buff which says something like "Calypso's Curse" this way it will also show up as a buff.
Besides that no real advantage