I had to google what cuttle bone was! Looked like a creepy bug egg in the pic. But now I remember seeing birds eat it. Seems like it could work/not hurt.... But I have never bothered with adding oyster shells to my pots. I prefer to just use feed that has calcium and magnesium. Be interesting to see if you think it does work though.
An Interesting idea!
Sepia has a sponge like structure of Aragonit and Chitin (insect shells) and lots of trace elements.
Oyster shell is mostly Calcit with a inner layer of Aragonit.
So both are chemically Ca CO3. Which cristaline structure is prefered by Paphs probably nobody knows.
The spongy structure of the cuttlefish bone might be an advantage...
Would be interesting to hear your experiences with it!