Ads are displayed several times when you are playing, but you can turn them off by purchasing the ad-block.
After making a purchase, all ads are removed from your account, except for the video-ads. These ads are optional for all players, including players who make purchases, since you only need to see these if you really want to open a chest after a match.
We understand it can get annoying after a while, but remember that you don't need to open all the chests you get! You always win coins after a match and also win free chests and coins from time to time.