In the Commander decks that want to have this available, it’s very strong. It’s no wonder then that many Red/Blue decks play it. According to EDHREC, about one-sixth of all possible decks in its database run Counterflux. With Mizzix of the Izmagus entering the fray as a strong Red/Blue Commander option, Counterflux has seen considerably increased play.
Wizards of the Coast made a good decision to print Counterflux in the Mizzix deck, Seize Control. While this takes what was a $1 rare and make it pretty much bulk, foils are around $5 and they have not been negatively affected. This is a fine choice to give more players access. As it is, Counterflux sees heavy play in the decks of Tibor and Lumia, Keranos, God of Storms, Niv-Mizzet the Firemind, Melek, Izzet Paragon, and Shu Yun, the Silent Tempest, plus many more. Red/Blue/White decks that utilize the Equipment Sunforger to seek out Red or White sorceries have Counterflux as one of their top choices. This includes the afforementioned Shu Yun, plus Numot, the Devestator, Ruhan of the Fomori, Narset, Enlightened Master, and Zedruu the Greathearted. Having copies be even more plentiful for a card from a set that is best known for Abrupt Decay, Deathrite Shaman, and shock lands is a good call.