Here is a crushing explanation about the importance of handling strong magnets carefully. These have a pull strength of 300kg whereas the ones I will be using for Hollow have a pull strength of 7.3kg. I've still managed to get a few blood blisters.
One incredible thing about Neodymium magnets is that once magnetised they remain magnets effectively permanently losing magnetism imperceptibly over a 100 years. They are easy to re-use but less easy to re-cycle.
Apparently the discovery of neodymium magnets in 1972 and has been a big factor in the advances in consumer electronics. They are in every speaker, microphone and telephone. They are all around us!