Oh, it's something new. In my case Truberbrook worked "as usual". I was able to check the price and use one of two options: Redeem and Cancel. Actually I always use Cancel as I need more time to decide if I want to use a code and make a purchase.
In this case there seems to be no such option, indeed. Redeem only, before the amount is displayed.
Often I am like, "I've never heard of that game, but the price is reasonable so I'll take a closer look at it later", but if I can't even see the discount amount without immediately having to make the decision to buy, I probably won't bother wasting time looking the game up.