A diameter of 30 mm is actually an absurd size for sphere magnets - each sphere has an adhesive force of over 13 kg! Ask a woman to separate two of them by hand; not many will succeed. And then you hand the spheres to a grinning guy and watch how his facial expression will change from bewildered to tense...
Such a large sphere magnet is not really useful, unless you can think of something? In that case we look forward to hearing from you.
As with all large sphere magnets, the surface coating will not last forever, since the point-shaped contact areas are exposed to enormous force.