If this is really true, why does Gillette advertise their high-end, multi-blade razors as multi-use? For their top product, they say "up to 20 comfortable shaves".

Sure, as you can also reuse single use razors.

But the main benefit of single use is reducing the chances of skin inflammation after using the razor.

If using single-use razors, I'd recommend replacing just the blades, not the razor.

You can't replace the blades on a single use razor any more than you can replace the bristles on a toothbrush

Sure, in this case you usually don't buy a single use razor, just the blades. The blades are sharp enough to use them multiple times, but if you don't want inflammation, then it's recommended to only use them once. Search for Wilkinson Sword blades.

Sorry to be that guy, but…

https://www.amazon.com.au/hello-Toothbrush-Replacement-Refil...

(And for the record, I think this is an absolutely stupid idea).