The main difference between Nip-46 and the Frostr method is that Nip-46 requires you to trust a bunker with you nsec or run your own while with frostr you can only provide the bunker with a single share of t-of-n FROST signature scheme. This way if the bunker was ever comprimised, you would not get rugged.
Discussion
how do shared secrets and encrypted notes/DMs work with frostr?
I think it's going to have to been handled with proxy keys that the client has full access to as I don't think that message decryption will work with frost. This may be better in the long run though as it should help prevent against metadata being linked to your main npub