This is an instant of hiding the critical information about the quality of the product. Imagine you buy a second handed laptop on ebay, and you were not told that the all the vowels on the keyboard are not working. Certainly that is a dishonest practice, even though it was not technically robbing, even though everyone know that second handed laptop have a chance of being malfunction one way or another. Same here, you were not told of the chance of receiving the capes, and that is a very critical information that will significantly alter the value of the box.
The difference is that you are not buying a product off ebay. In which you get the description of the product and have the right to return it if you did not receive what you paid for. You are not buying a product, you are gambling for it.
You are placing money into a box which gives you the CHANCE to win one of what 6 items? Do you demand that the owner of a casino tell you the chances of getting straight 7s on his slot machine is before you play it? By putting your money in the box you are taking away any right to claim you were robbed. If at all you were "robbed" the same way people who play the slots for hours get robbed. Either way, it is all by choice. You are not being forced to spend a penny therefore Aeria is not doing anything wrong. :\
You guys are putting way too much into this. Should you like what is offered and willing to gamble for it, then good for you. If you find that it is not worth the chance, then don't put forth your money. That simple. No need to complicate things.
Mystery Boxes= Slot Machines