I carried bear mace with me while I was in Alaska four years ago. I was hiking and fishing out there and I was all by myself. Thankfully, I never had to use the mace. I will, however, tell you that it added to my peace of mind. I saw some paw prints that were as big as a dinner plate.
Now I keep the mace in the house. It is, in my mind, a great home defense tool. If someone is breaking into my house I would never shoot them. I am not a fan of using guns for home defense. I would, however, mace an intruder with glee.
I have also spent some time in Glacier National Park. I met many, many locals there that carried bear mace. I never met anyone that had actually used their mace on a bear.
The reports on bear mace are mixed. In some cases the mace has successfully deterred black and brown bears. In some cases it has not. It is better than nothing - in my mind anyway.
Don't listen to people that tell you that capsicum (one of the active ingredients in the mace) attracts bears.
I know a guy that was maced with bear mace and his experience (terrible stinging, vomitting and pain) attests to the fact that bear mace is nothing but miserable.