No, they are not absolutely mandatory, but we always recommend you use either glue or set screws in your Hovr installations.
If you opt not to use glue OR set screws, and whatever items you later place on your finished shelf do not have sufficient weight to guarantee no one can lift it or make it jump up by bumping it, it will come off the wall when hit from below (Hovr cannot take responsibility in this case).
Essentially, the Hovr bracket system is a French cleat but supercharged, and still needs to be secured in some way once the two components are connected. Please always use one or the other.
We urge you to always use set screws in order to get the strongest, most secure installation of your Hovr bracket, as glue cannot maintain the same level of strength and hold and is also a more permanent solution - with set screws, you can always remove your shelf to replace it or set it up elsewhere.
Need to order extras? You can buy sets of 50 additional set screws here.
If you are interested in learning more about how to glue the aluminum bracket instead, you can read about it here.