Bear in mind that some of your more elderly relos might have heart related hardware that might be damaged by a strong magnetic field. Luckily ... inverse squared law. You are probably safe if you recommend that granddad (1) doesn't rub his chest on your fridge.

I have loads of the bloody things - I dismantled a Equallogic PS6something that had 30 odd discs in it for recycling the other day. I, sorry: "we" still have four more old Eqls and a stack of discs removed from old PCs. You can break the case of a 3.5" disc with a lump hammer and cold chisel and then unscrew or break out the magnets quite quickly. I need to look into breaking a 2.5" disc. You could speed things up with a bandsaw with a suitable blade and a careful cut.

(1) I'm called Granddad by two little girls, so let's ditch the ageist bollocks (po faced emoji). How about great granddad instead! My dad does sport a heart restart device (I can't remember the name) and it is probably not going to work very well after close contact with a neodymium magnet that nearly tore off one of my fingernails - OK I nearly did the tearing but it was the vice that did the holding with my fridge.

[edit - formatting]