Regardless of ad vendor, ads have to be downloaded from some network server. This is a CPU activity (not our GPU graphics pipeline). many factors impact the download and rendering speed of the ad and all of this is on the CPU. I can’t find the link, but Google recommends not showing banner ads when frame rate matters.
There is a second part of this that you should consider. You get paid for people tapping on banner ads. You make almost nothing from showing a banner ad. Ask your self, how often are your players going to stop, interact with a banner ad in the middle of game play? For some games, for instance Angry Birds, Word with Friends, etc. there is time when the game isn’t doing anything (waiting to launch your bird, trying to find the right letters to use, etc.). In these type games, there is time for the player to look at the banner ad and interact with it. These are also games where loading times don’t affect game play. But if you’re building an endless runner, a platformer, a shooter of some sort, your player’s eyes are not going to look at the ads and if they do and tap on an add, they will end up with a level over/failed situation because they lost attention. And these types of games are more CPU intensive and you’re going to feel the banner ad.
So what you end up with is an app that burns through the ad provider’s fill. It’s not helping them, it’s not helping you. You’re much better off showing an interstitial ad between levels and banners on menu screens, high score screens etc. when the game is paused and the banner ad can be effective.
Rob