This BIP 85 thing is amazing.

I did know it existed.

Thank you.

So I can create many online wallets from my master seed?

And it's safe?

And the only thing I need to recover is the index number?

Amazing.

If there any downside or risk?

Is it really safe to recover an online a wallet from 12 words bip39 created as a child index 0 from my precious cold offline secret seed?