Following on from the thread on the 18th edition wiring regulations,
does anyone have any comments on whether these devices are a good
idea, or if they are more intended for industrial premises with
machinery running unattended?

Is it one per supply or one per circuit?

My assumption is that arcing would not trip an RCD/RCBO because there
is no leakage to earth and would not trip a 'fuse' because the current
may not exceed the rating (eg 32 amps). Is this broadly correct?