Never trust a private key that has been engraved.
As opposed to what, printed and placed under a hologram?
- Engravers need to be programmed and you need to trust that programming is wiped. If you hire someone to do it because good engraving equipment is expensive then you have to trust their setup and that they did not save the programming intentionally or unintentionally. Only real way is to use an air-gaped system and properly wipe it after.
- any imperfections on a metal surface can be seen using imaging equipment hologram or no hologram.
As opposed to an affordable printer that can be destroyed when done or one that doesn't save jobs to memory.