I wrote here an articole about Agar on Android and already told you guys how much I hate people that try to play agar.io with cheats 🙂
If you are interested in playing agar.io on your iOS smartphone, you actually don’t need to worry about the fact that right now there isn’t an official version of Agar for iOS.
The app that you can see on their official website (agar.io) works pretty fine on iOS and Android too. I checked it on a Nokia Lumnia 520 too and I can confirm that is working ok on Windows Phones too.
PS: If in the meantime they will develop a dedicated iOS version for agar.io, please let me know about to update this post.