First off the picture for the app is very wrong as there is no turrets in the game. It also says "30 levels!" lies, they give you 20 levels and ask for money if you want ten more. Within the first few missions of the game you have already unlocked all the towers as there are only 5. Also there are no options and nothing as far as upgrades. If you want a good tower defense game, get Block Fortress War, or get Block Fortress.
Metthroid about Block Defender: The Pixel Defense 3D & HD