Like most Magic: The Gathering cards, the value of Mana Leak depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Magic Player Rewards 2005)
There are some incredibly powerful new cards that will have big effects on the meta, plus some brilliant art
A spread of packs from every single Sun & Moon set
The strategy is damn hard to disrupt, to the point that official tournaments were seeing 40+ percent of the field running the exact same archetype
Obviously, buying yourself a little time is useful, but another possible part of the equation is that, unlike most of these two-cost cantrip artifacts, this one can sacrifice itself every turn
Characters with Ward like Jetsam, Riffraff and Flotsam, Riffraff (if you have Jetsam in play) are particularly sticky , while Evasive characters like Don Karnage, Prince of Pirates and Wildcat, Mechanic can be hard for your opponent to remove