Hi,
With the release of Titan Turret 1.6, we've made some ground-breaking changes.
Enter the Titan Turret Shop! The shop allows players to upgrade their turret or buy power-ups with Titan Coins and XP. XP can be earned by simply playing the game while Titan Coins can be earned or bought. There are various ways to earn Titan Coins. First, a player can earn achievements. Each achievement rewards the player with Titan Coins. The second way to earn Titan Coins is to make use of advertising partner's ads.
You can earn Titan Coins by installing and playing advertised Android games. Yes, that's right this means earning Titan Coins while playing games.

No restrictions, no fee's, no hidden legal mumbo-jumbo; play an advertised game and earn coins! Awesome!
We expect that our younger players will benefit the most from this change. A credit card, or money for that matter, is no longer required to unlock the entire game.
Al always, feedback is more than welcome!
Thanks!