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.