ND filter for the Obsidian.
The ND4 filter is designed to fit the Obsidian, reducing the light coming into the Obsidian's sensor and help avoid over exposure on photos.
The ND4 filter allows 1/4 of incoming light through, equal to a 2-stop filter.
You need a drone license when you are flying as a commercial drone pilot, ie when you are using your drone for work and money-making purposes. This means, in most cases, you will need to sit the FAA Part 107 test.
You do not need a drone license when you are flying as a hobby and for purely recreational purposes. However, you will need to operate by strict rules. There are plans to introduce the requirement for hobbyists to pass an online aeronautical knowledge and safety test.