As far as I understand, the email is quite important, as you would get notifications there that you have to catch in case of a delayed cosign event, etc. Thus, you would usually have to install the app from the mail provider, turn on notifications, etc., and by doing this, link the device to your "identity/location". So, IMO, the moment the Nunchuk database leaks, an "attacker" would see all emails/clients, including their related balances, and then decide if it's worth locating this customer. So, at least to me, this seems like a lot of personal risks added for the purpose of inheritance or simply because you want a kind of other signer in your setup (iron hand plan). All this would be mitigated in big parts, IMO, by adopting chain delegation, etc.

Don't get me wrong, I don't want to talk bad about the product. I personally look to upgrade my multisig after the recent events and came to Nunchuk through this and am evaluating pros/cons now, but for me, if I get it right, at the moment it seems like it would at least for me create more headache than it solves. If they could offer the same service without these issues, which seems technically possible (chain delegation), it would be an easy yes for me, I assume.