Hawk:
To answer your questions;
First, the three sections of the ASP all taper towards the front.
When you extend the ASP, forcefully, the front section (the heaviest) moves forward, when it reaches the limit of its travel (it's widest point is at the narrowest point of the second section)
the next section begins its motion and then the third piece does likewise. How tightly the pieces lock open is directly related to how much force is exerted when you open it. When you tap downward on the tip, you are forcing the front section backward, into the second section and so on. I hope this makes sense.
Second, the most popular would have to be the 21-inch steel, black chrome, foam handle model. It's the most prevalent in law enforcement circles, IME. Next most popular would probably be the 26-inch version of the same. The Airweight models use the same steel striking section as the steel batons, but the middle section and handle are aluminum. Airweight models aren't really intended for uniform carry. ASP has offered the silver chrome and electroless nickel finishes for many years for both product lines (steel & airweight). Several years back ASP began marketing the Airweight models only with the electrless nickel finish. This was to alleviate the problem with the Airweights seizing open when opened forcefully. It appears to have solved the problem.
I own several different collaspable batons from many different vendors and, honestly, I think the ASP is one of the best executed designs out there. I carry a 21-inch DuraTec which is ASP-speak for an Airweight, Rubber Handle model. If you are interested in the steel models, I'd suggest looking at the Monadnock AutoLock line which has a very slick, very different locking/unlocking mechanism.
The ASP training program was actually developed by Leo Gaje Jr, many moons ago. Leo Gaje Jr is a phenomenal practicioner and the developer of the Filipino martial art known as Pekiti Tersia Kali. Since you live in the Dallas area, you are lucky because there are many competant practicioners of various FMA all over the city. Check them out, I'm sure that you'll be quite impressed with what you can do with a little one pound stick.
Oh, yeah, the only real difference between an ASP and a wooden stick is that most people won't notice you walking into a movie theater with an ASP tucked in your beltline. A 24-inch piece of "Old hickory" on the other hand.....
Gomez