Many years ago I built a power supply (an Elektor design) which used a 78HGKC voltage regulator. The data sheet explicitly said not to open the TO3 package as beryllium oxide (BeO) was used for thermal transfer.
Today I learnt that BeO ceramic can be used as an insulator in magnetrons in domestic microwave ovens, e.g. YouTube: DIY How To Disassemble A Magnetron.
Beryllium copper alloy is used in high-quality connectors for test equipment.
Berylliosis is currently incurable.
If I were to make something containing beryllium compounds, even though it does not come under RoHS regulations, should I only say so in the product datasheet, put a notice in the equipment, or just say nothing?