The up side and dow. Side to nostr nesec ...down side if somone gets that they can access certain stuff...upside they cant change that so youll still at least allways have accessto your account. For perspectiveif somone gets your nsec its not like somone getting your password to facebook. Reason being is they can chsnge your facebook password and lock you out and they cant do that with nostr.
On amethyst i know for sure you can encryt your nsec with a password so helps with securing your nsec. But just know as far as i know as long as you have your nsec your never locked out .