Counterbalance Top allows you to have a great game against Zoo, and many other decks in the format. Not only can you play "Protect the Nought," which is helpful in and of itself, you can also end the game for some decks, then lay down the Nought.

CB-Top allows you to have a decent game against Zoo if you can get it online. You can counter all their 1 drops most of the time, so they can't burn you out. Kira doesn't protect you from being burned in the face and killed. They can just go "Bolt, Chain lightning, Bolt, Price of Progress, Fireblast. Win?"

CB-Top also gives you a real edge against Combo. Most of the time, Combo either tries to take your Force of Will, or build up enough protection and play so many things you can't counter them all, then they Chant you. With CB-Top on board, you just counter their relevant spells with CB, then hard counter spells you can't touch (ex. Iggy) with real counters.

It is a bit slow, I'll be honest. I'm not as much of a fan as I am having something else, but it is very good against a variety of matchups, I still keep it in because its just SO good against so many things, it can be better than having extra Engineered Explosives or what have you.

Hope this helps!

-Matt