Max,
There's a difference between OC (oleoresin capsicum) spray and mace. Between the two, I'd get, and use at work, OC spray. To my knowledge, bear spray is OC and not mace, at least my bear spray is.
If you buy the stuff for self defense against humans, typically your range is going to be 12 feet. Maybe more if you buy a canister with stream pattern and maybe less if you buy a cannister with conical mist/fog pattern. If that's all you had, and you wanted a multi purpose item for the front country, that might work against a lumbering curious bear but I'd hate to bet my life on it if I was at the receiving end of a bear charge. If you're going to carry anything, I'd stick with purpose built bear spray which typically has a range out to 30 or so feet.
I think there have been some fair comparisons made here, dogs being one of them. I encounter hundreds of dogs, 99.9999% of those encounters are fine, but occasionally there's an exception. A lady from my organization, who I don't know personally, was medically retired after being attacked by a Rottweiler and now suffers from permanent nerve damage in her leg. She was in pretty bad shape and the dog is smaller than most sub aduot bears.
Another comparison I'll make are seat belts. I'm 44 years old and have never been in a serious accident. I could have gone my whole life without wearing one, but click in every time I'm in a car because the risk isn't worth it for me. This is a decision I make multiple times per day that isn't based on fear, but risk mitigation.
Another thing to consider is that bear spray could save a bear's life. A nuisance bear who learns to fear and avoid humans after being sprayed is better than a nuisance bear who later becomes aggressive and gets shot by a fish and wildlife officer, as wa the case recently near JBLM.
It's highly unlikely that you'll ever get attacked by a bear, but if you ever are, bear spray is by far the best defense. I have access to several firearms, including a mil spec M4, and would always grab my bear spray first as that's my best chance for survival.
I carry OC spray most days at work. I once ruptured a canister after doing a belly flop in a parking lot during a foot pursuit. Other than this single incidence, I have thousands of days where I haven't had a problem with it. Whether or not you'll have a bad experience from a negligent discharge is totally up to you. Show a minimum amount of care, and you'll be fine. Attach it to your ruck and carelessly throw it onto a tour bus, and you may find yourself tarred and feathered by your fellow passengers.
Edit typos ala fat thumbs on iPad. Deal with it.