Is Hex worth it at high levels?

[Psyren]

Perhaps an Invocation?

Evil Eye
Prerequisite: Must know hex.
When you cast hex, you may choose to have your left eye take on a supernatural appearance denoting its vile power. It may have its sclera turn black or crimson, continually drip tears of blood, glow with power, or any other mark of its supernatural charge. If you do, then you do not need to concentrate on this casting of hex. If you cast hex again for any reason, any casting maintained by your evil eye ends.

I like it but would tweak it slightly; "your concentration on this casting of Hex does not prevent you from concentrating on another spell or effect." Similar functionality (you can have Hex and another concentration effect active simultaneously) but it would still be possible to lose concentration on it due to damage or incapacitation. I'd also add the Subtle mechanic into this invocation since the eye's appearance itself would be enough to enable counterplay.