i think metamask still better than insert private key on exchange like etherdelta or idex. if u want safer u can buy hardware wallet like ledger or trezor.
very correct, it is true for now this is a very good metamask for its security than others, such as private key, and jason file, if in my opinion is still better metamask, so to hack hard, because the security is very high, my advice do not save the private key in the forlder without creating a password.