These will provide you with 1 - 3 star characters from the 2 specialty classes (Gunner or Assassin). These are not nearly as common and are typically gathered by purchasing them in the trooper store.
When you open these, you'll typically find some 1*, 2* and 3* characters. Again, these are going to be characters with abilities you may want down the road, so keeping one is never a bad idea. They can also be useful for some missions where you need to use all one class of character, so keep that in mind as well.