AdMob or AdMob free?

Hi guys,
I’d like to add adv to my app but I have 2 questions.

  1. What is the difference between AdMob and AdMob free?

  2. On Google AdMob platform I created 2 different Application. One for iOS and one for Andorid platform. Is it the best approach? In this case I will have 2 different ADMOB_APP_ID and so 2 different banner id, one for each platform. I will need to have a platform specific setup in my app.

Thanks in advance to everyone