It is not the worst value when it is at it worst, still just better than Air Elemental
Mithril Coat If youre a Lightning Greaves kind of player, Mithril Coat has to be in the conversation now
This then gives you two ways to get your win condition on the board
Most commonly, they grant +1/+1 to all your other merfolk, but many do even more, like giving abilities (such as islandwalk or ward), drawing you cards, or making your spells cheaper
Compare with Birthing Pod from New Phyrexia (an artifact with 3+Phyrexian Green Mana casting cost, activation: 1+Phyrexian Green Mana, Tap, Sacrifice a creature: Search your library for a creature card with converted mana cost equal to 1 plus the sacrificed creature's converted mana cost, put that card onto the battlefield, then shuffle your library