As long as neither player is manipulating their library or using their graveyard, using a Millstone does nothing but reveal information until the player being milled runs out of cards, but it took more explanation than you can possibly imagine to make players understand this
In general, if you have a cheap removal spell in hand, its fine to give it the two +1/+1 counters
While the power level of creature-based decks has grown, control has fallen a bit behind
Outside of Standard, there are several other formats that players can explore in Magic: The Gathering , including Modern that encompasses many of the older sets, and the free-for-all format Commander
Im definitely always in favor of cards that can punish the prevalence of green ramp and this one offers a tangible reward in the form of your own temporary mana acceleration