Dave, I don't know much about the different brands of bear spray, but I have lived in bear country most of my life.
First, I think the stories about finding bells and pepper spray cans in bear bellies or in bear dung (that's the version I'd heard) are pretty doubtful. Bears do attack people every year, but they rarely get a chance to actually eat what they kill, when they kill a person.
Second, let me tell you a story about something I once watched. I was sitting on a hill above Russel's Creek in Cold Bay, Alaska, looking for good places to set some mink traps when the season rolled around. I saw a bear on the other side of the creek, in the alders, just a little way up the creek from where I'd been fishing earlier. I watched him for a while, and saw that he was sniffing about. Suddenly, he started jumping about like crazy, swatting at the alders, and he flattened a little circle in the alders, and headed across the creek. I went back to the ford, fast, because I didn't want to run into him.
A couple of days later, I went up into those alders with my trapping partner, and we stumbled on that ``little'' circle in the alders. It was close to 30 feet in diameter, and the alder trunks the bear had smashed were 1 to 3 inches in diameter. I didn't think he was a big bear; I thought he was well under 1000 pounds. Even though he'd only been jumping around for what seemed like a few seconds, he'd done a lot of damage.
We don't know exactly what had set the bear off, but I suspected that he'd stuck his nose down a hole and gotten it bitten. What I do know is that if you are within 15 feet of an angry bear, you could be in serious trouble, even if he can't see or smell you. That bear had destroyed everthing within about 15 feet of where he got his nose bit (or whatever it was).
I've thought about that every time I've thought about getting some bear spray, and I've always settled for my 45-70 lever action. That'll spray something that just might discourage a bear, if I can connect.
I've never had any trouble with bears, but if I'm going somewhere I'm likely to run into brownies, I always take something which can break a shoulder bone if I can put a shot in the right place. I also take bells, because most bears will avoid trouble if they can. I stay alert, because there have been well documented cases of bears that went looking for trouble.
Nels