That’s what I found when I just for laughs and giggles tried one out a long time ago; actually I was too lazy to change the insert back to steel after working in ALU. I only had one tool holder at the time…
If you try inserts for SS on hot rolled steel, you will also see an improvement vs a regular steel insert (when taking light cuts).
I wondered that too. So I have some inserts for stainless on order.
My biggest concern is that SS inserts may vary considerably in their design and some may be sharper than others.