Hafler also did that in the DH200 back in the 70s.
Personally, I don't like fuses in the amplifier output at all, but if a proper relay protector (DC, over-current, temp etc) isn't in the budget, something is better than nothing. Might as well attempt to ameliorate its effects and keep it in the NFB loop.
HK had a thing for self re-settable thermal cutouts at one point too in the 70s and 80s. They unfortunately became a source of trouble as their internal contacts oxidized. NAD even used them in the original 3020 IIRC.
Here's the PM-640 with the cutout in the NFB loop (tone controls also in the loop- not shown to left).
NAD 3020:
In the loop.
@SIY So if the fuse is of a reasonable linearity, adequately high in value (to carry the maximum planned load) and resides inside the NFB loop of a fast enough amplifier, what would you expect to see in low level THD contribution? For example, if we took say the Benchmark and put a 7.5A(F) fuse in line and kept it in the feedback loop? Would be be looking at just increased THD at very low levels where the contact oxide (breakthrough) resistance comes into play from the fuse holders etc?
What about if we extend the feedback loop (a la Kenwood Sigma Drive circa 1980s) all the way to the loudspeaker terminals themselves and take the speaker cable out too? Have you ever experimented with feedback at the speaker terminals or negative impedance drive (lifting the 0v) and putting the driver in the loop? I have. It wasn't pretty.
Yamaha managed the so-called 'negative impedance drive' quite successfully with their AST (active servo technology) in the early 1990s. Combined with very basic crossovers and response matching cartridges (which plugged into the integrated amplifiers, customized for each speaker), they could achieve some phenomenal sounding combinations with very compact speakers. It didn't take off and we ended up selling the entire range very cheaply. People would lose the 'flat' cartridges and/or the ones that came with the speakers. They'd sell the speakers and forget to give the new buyer the cartridge which was still in the back of their amp etc. Great idea, but still-born.