Random keys are fun to get to see what you get. Sometimes they are worth it and other times they are not worth it because sometimes you get games that are not worth the value and pretty much waste money on it.
Not all of them are like this but sometimes it is and often times, you may get duplicate keys if you get more than one, you can always tell them this when you purchase so they can change it out or you can give them to people who want them.
I often times just take them and give them away to friends. Some also gives you random items for games. This is sort of like a mystery box and I love the idea of this since you never know what it is nor what you are going to get.