I'm not sure I understand it completely, please help!
Dear Mr. Spangles,
Thank you for your patience.
We have an answer from Switzerland saying that this model is in transition of changing parts into silicon. There will some of them in the market still are not silicon. Model's detail stating with annular balance is non-Silicon, if it is a Breguet balance, that will be silicon.
That is the answer given from Switzerland.
Sometime visually we can point out the differences
I hope this answer will help your decision in choosing 5817model.
Best regards,