The energy of a crystal ball radiates in all directions and is generally used to improve the geomantic omen in a certain place. The crystal cluster can degauss and purify the magnetic field, and the energy is relatively restrained. There is no comparability of energy between the two, mainly because of the different forms of energy divergence.
As for degaussing, it is better to use sunlight because it is relatively large, but colored crystals like amethyst will fade in the sun, and it is better to use moonlight or sea salt.