You are right, I did miss that. A hex might be fun to try to convert, but a lot of work that could be better spent elsewhere.
Back to your original question: That skimmer can only be used in a sump. There are hang-on-back (HOB) skimmers, but for the most part they are not very effective. After your tank is up and going (cycled, and populated) you would add the skimmer, but not before. What kind of lights do you have for the 50 gallon tank? That will determine what kind of corals you can house.