It's an excellent answer to an opposing combo, and circumvents most counterspells since your opponents can't cast anything in response
On the flipside, if your key engine costs a ton of mana, like Kozilek, the Great Distortion, a big beefy ramp card like Thran Dynamo will get Kozilek out much earlier than a Mind Stone
Beyond the names and creatures youd expect, this extends to creatures such as Bill the Pony
Four mana is accessible early without issue in green, and the payoff is well worth the price of admission
Knowing youre the only one that can play combat tricks or removal spells during combat makes it much easier to decide who to attack with what creatures
At five mana youre not going to get this flipped before turn 6 at the earliest, but thats about when youre confidently in second spell category anyways