On the pepper spray front, I happen to like it as a carry option or accessory; some very experienced people do not. Like any tool, it requires some information and training to be effective. And what follows is just my opinion--take none of it as truth, just as hints for research.
For me, first and foremost, is the delivery mechanism. Aerosol mist or "cloud" should be right out of the question unless it has a powerful and focused pressure system that can reliably expel the mist in a tight cone until well away from the user. Even with no breeze at all, with a cheap aerosol mist you stand an excellent chance of being part of that cloud yourself if you employ it.
And that's one of the two biggest problems with OC (Oleoresin Capsicum, not Open Carry): if you use it, you stand a very good chance of getting some on yourself. If you carry OC, always carry a couple of decontamination wipes in a pocket. Most of what you'll find are Sudecon towelettes in a sealed packet; a little larger than the size of a packet of sugar, they unfold to an 8"x12" towelette.
It's not just the risk of a big aerosol cloud. Even if you use a stream delivery (it's like aiming wasp spray and can be reasonably accurate out to 10 or 15 feet) and hit your mark with a nice dose, a committed attacker can keep on comin'. If you then have to make physical contact to ward him off, it's easy to transfer OC onto yourself. If you're sensitive to capsaicin, even with the Sudecon wipes handy it can be two to five minutes before you'll want to try opening your eyes if you get OC in them.
Spray, get away, then wipe down your face and hands, even if you don't feel any effects. Don't take a chance on rubbing your eyes with fingers that may have OC on them.
And for that very reason, OC becomes a poor option if you're at extreme close contact distance. If the BG grabs you by the throat, for example, a spray to his face is almost certain to blow back on you. It might be worth the risk if you decide that's your only choice, but it's always best to get a couple feet clearance before deploying a spray.
That segues to problem number two: OC affects different people in different ways, and you can't count on it to be a fight-stopper. A small minority of the population seem to tolerate capsaicin fairly well, and a junkie amped up on various chemical cocktails may have a very different reaction to it than he might otherwise. So you need to consider OC as distraction in an encounter: a tool to break the BG's OODA Loop, but not as a tool that will disable the attacker. You have to be immediately prepared to follow-up or flee.
After choosing a delivery system, the next consideration is potential effectiveness of the particular brand of OC. There are a lot more on the market than there were 20 years ago, and choice isn't always a good thing.
We have Wilbur Scoville to thank for the measurement that is most important to us. He developed what he called the Scovill Organaleptic Test, what we know today as a measurement called the Scoville Heat Unit (SHU). We've gone way beyond Wilbur's 1912 test, however. Today SHU is measured by a standardized liquid chromatography test; no subjectivity involved. Relatively speaking, a non-pickled jalapeno comes in around 5,000 SHUs; a habanero in the 250,000 range; and pure, pharmaceutical capsaicin at around 15 million. You can't buy it at that concentration in a spray, and you certainly wouldn't want to play with pure capsaicin at home.
My advice would be to ignore any product claims regarding the percentage of oleoresin capsicum in the spray. That percentage figure can swing wildly from 1% to over 20%, but it really doesn't tell you very much because it doesn't measure the relative "heat" index. Not all sources of capsicum are the same, and judging by volume just doesn't work. For example, I have a two-ounce canister of Fox "Five Point Three" stream-delivered OC. It states 2% oleoresin capsicum and 5.3 million SHU. I've seen "bear spray" stated at 18% OC but less than 2 million SHU.
The more a product talks about the percentage of OC in its spray and avoids the actual SHU value, the more I'd be wary of it.
ASP makes an interesting product that you might want to consider:
http://asp-usa-demo.com/oc.html:
It isn't a stream delivery, and it's about 2 million SHU, so not the best choice for me on either count. But its delivery nozzle is first-rate and, made of aircraft-grade aluminum, it doubles as a Kubotan or Yawara stick. It's slim, can be carried easily in a pocket, and doesn't look like a conventional pepper spray canister if carried on a keychain.
