Don't quote me on this, but I think that's the minimal size that can be legally sold as "bear spray". From what I know, you're supposed to use an entire can during one spray, too. You wouldn't want to be shy about hosing a big bruin in the face.

Compared to other forms of protection (big guns, electric fences), that's pretty lightweight insurance. It's probably the best option for most people. I've not direct experience with bear spray, but all of the studies and anecdotal evidence I've heard have been very positive.

The only negative thing I've heard about it is that it can attract bears to the area after the can's been used, even the bear that got sprayed. This might be a myth; dunno. If spray gets used (on purpose or otherwise), it'd be a good idea to stash the can in a odor proof sack along with your food & toiletries.