think Kryoflux can also wipe the disk completely, and maybe other tools can as well (SCP or GW)
No, it cannot. While Kryoflux promises to do so, it does not according to my experience. Look at the following images:
This is what a track erased with Kryoflux looks like:
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For comparison a track erased with the SuperCard Pro (same floppy + floppy drive used):
Bitte melde dich an, um diesen Anhang zu sehen.
The images were created with the SuperCard Pro + associated software.
Just imagine that the above is scattered from the neighboring half track into the wider read/write head of the 1541... if it should come to problems, I would have no more questions.
BTW: From such an SCP deleted track, kryoflux just reports "communication error", probably meaning "timeout". I suppose this is because it (the kryoflux hardware) only emits bytes with Flux and with Out Of Stream packets. So one whole turn nothing, then an index comes again. Quite reasonable to assume a timeout.
A magnet will not work well enough, it just makes a mess.
Really worse than Kryoflux (1st image)?