You have to be in the right mood and willing to do the work to sift through SM's posts to find the diamonds in there. He's not trying to be rude; that's just the way he writes.
If you're determined to use a knife for self-defense, then it needs to be big enough, sharp enough, strong enough and carried enough. You already have some idea of these requirements.
1. Big enough: Opinions will vary. Almost no one on any internet forum has actual experience drawing blood intentionally with a knife, so you'll get more opinions than solid "This worked for me" information. Personally, I carry anything from a 3.5" to a 5.5" blade. I like my megafolder, but I carry the flattest one I've found available and it's still bigger than many people would want to carry every day. Probably not legal in California, either.
Someone will inevitably mention the minimum length needed to stab vital organs. Maybe that's important to you, but I see a defensive knife as a way to cut my way loose. I don't really mind a shorter blade for that reason as long as it's sharp.
2. Strong enough: This is where the S&W knives might let you down. I believe they're still made by Taylor Cutlery, and not to the highest quality standards. IF you are certain you want a folder, I'd look at Benchmade and Spyderco first. If neither has something you like, you should by then have a pretty specific knife in mind and you can find it elsewhere. Right now I rotate between a Camillus (that's the megafolder, and unfortunately they're out of business) a Spyderco, a Benchmade and a Kershaw on a daily basis. But I'm a knife weirdo and all mine get used for daily cutting; if you're serious about using your knife as a dedicated weapon you're better off learning one model and using just that one.
3. Sharp enough: The brands I've recommended all come shaving-sharp out of the box. After that, it's up to you. If you're going to be using your knife for your daily chores (envelopes, string, apples, etc.) then you'll need to touch it up often to keep it sharp. It needs to be awfully sharp in order to, for example, be ready to slash through clothing to damage the arm that's holding you. Again, if you're one of those guys who's carrying the knife solely as a weapon, you won't really care whether it holds an edge or not, since you won't dull it by using it to cut open boxes and envelopes and apples.
4. Carried enough: It does have to be comfortable and small enough that you'll carry the thing. For that purpose it's best if you can visit a cutlery shop. I don't know of one in California, but I'll bet there are some around. That will let you handle a lot of knives and see how they carry in the pocket.
5. California has weird rules about concealment and blade length. Check this out:
http://pweb.netcom.com/~brlevine/ca.txt
That's a link to Bernard Levine's website. The blurb linked is the text of California's knife statute, but click over the main site for lots more good stuff about knives and the law. Then you'll know, and knowing is half the battle.