It's maybe an 8 or 8.5. While it is max defense, the "while hexed" clause kinda sucks and -1 damage isn't particularly large. If I were you, I'd throw out the shield and get one with an ability you can easily use (like -3 dmg while HP is >50%) instead of "while hexed."
Depends, I'd give it a 9. It's a max armor strength based shield. That's important, because I'm guessing your warriors has 9 or 10 (at least) points in strength. Tactics based shields are always inferior.
the hex thing...eh, well, I'd just hang on to it until a better one comes along. That's what I am doing right now with my 16 armor (8 Strength) sheild of preciousness.
Yeah, it's hard to put these things on a scale. If the scale includes ALL shields, well, merely being maximum armor makes it better than most shields, making it almost at LEAST a 9.
But if you are comparing it among only maximum armor shields, it's pretty lousy.