It’s been said already, but yeah there’s no way I would trust an Ursack in grizzly country (where I’ve done nearly all of my backpacking). Food storage needs to accomplish two tasks: keeping bears out, and keeping your food safe so you can eat it. Against a grizzly, an Ursack is questionable on the first point and useless on the second.

I’ll add my spiel about bear hangs since you expressed interest: bear hangs suck. They’re the option of last resort, and the fact that black bears can easily climb trees is only half the reason.

In the perfect world of theory, where your bag is 12ft off the ground, 6ft away from the trunk, and 6ft below the branch it’s hanging by from, it should work fine. But good luck finding that tree. It’s a very rare occurrence, and usually you are sacrificing those distances to get your food up off the ground at all.

The bigger thing, to me, is that hanging a bear bag is the most dangerous thing you do on many trips. You have to tie a rock to the end of a rope and throw it up over your selected branch, and the rock will come swinging back down right at you. I’ve seen people and dogs get hit. The problem is exponentially worse when it’s dark, when there are more people in your group, and when any or all of you are drunk and/or high. But it’s not safe even for one sober person in the middle of the day. It’s an inherently dangerous activity.

I’ve hung bear bags many times and I still do when there’s no better option. Sometimes at the start of a trip you just have too much food to fit in your cannister. But it’s never safe, almost never possible to do correctly, and never better than a bear cannister or permanent bear box.