Plot Twist Cards [RPG]

The premise behind Plot Twist Cards for Pathfinder is that they allow players to influence the story in ways other than what their character directly does.  Each card has a theme, a picture to accompany the theme, a flat mechanical effect, and then four plot-related suggestions that could happen.  For example, the "Bad News" card shows a picture of a burning building, has the flat mechanical effect of "Target gets a -4 penalty on a single roll", and then has these plot suggestions:  "A messenger brings bad news", "An ally faces peril or death", "A favorite refuge is destroyed", and "Something important is stolen."  Players can use the card either for the flat mechanical effect or for one of the story suggestions; the latter use requires GM interpretation and decision-making, and the instructions are quite clear that the GM should feel free to modify the suggestion (or even refuse it) as necessary for the story.  The deck comes with 51 different plot twist cards, two cards of rules, a card with the Open Gaming License, and a card that's an advertisement for other products.

I've been using the Plot Twist Cards for about 20 sessions while running an adventure path.  Instead of giving one to a player every time their PC levels up (as per the instruction card), I've been more cautious and handed out one to every player at the beginning of each chapter of the AP (and drawing one myself to use against them!), with unused cards going back in the deck.  My players have used the cards to do some fun things, like have the "Broken" card cause the floor of an abandoned building to crack open, the "Sanity Check" card to have a tentacled water monster appear in the river, etc.  In my limited experience, PCs don't use the flat mechanical bonuses and instead use the plot suggestions, saving the cards for when they're needed in an important fight and centering their suggestions on things that can hamper the enemies or help their allies.  On the whole, I'm of mixed feelings about them.  I really like the surprising twists that the card facilitates and it's great for the players to have a little something hidden away for a rainy day.  On the other hand, it's often challenging as a GM to interpret the card and the player's suggested twist in a way that respects the integrity of the concept while also being careful not to trivialize an important encounter.  I think I would suggest the cards are good for a group that is a little easy-going and understands the role of GM discretion, but they'd be a bad idea for a very strict "Rules as Written" group.