Saw this reference to Frontier pay-to-play model in another app review (for Hearthstone):
http://www.computerandvideogames.com...ft-ios-review/
When talking about its free-to-play model:
"Some might point to far worse offenders, like EA's Dungeon Keeper or Ubisoft's Trials Frontier, to offer a sense of perspective on how free-to-play is truly misused."
...being mentioned in the same breath as the notorious Dungeon Keeper is rather embarrassing...

