Are you sure that gathering data without your players knowing about it is a good idea? As you are skilled in programming, why not add an interview form at the end of your game and ask them what they liked/disliked about it? I, as a player, would appreciate it more than you spying on me without my knowing.
It isn't completely unmentioned, rather it would gather data that a form would have problems telling me. Such as what choices the player made throughout the game, how often the player reloaded to change their choice immediately after making a choice. I don't mind adding an opt in button. I just rather not break immersion or confuse a player when a new window suddenly pops up.