The rhythm is much easier to maintain and the efficiency goes up dramatically when they are used as a pair. There's no point in leaving half your body out of the equation.
The most important aspect as you go up in price is you get the spring-loaded model, which takes some of the shock off your elbows and shoulders, and they get lighter. It's like anything else: People are skeptical in the beginning, and they won't invest in the over-$100 pole. They start at $65, and eventually upgrade.
They will actually allow people who thought they'd have to give up hiking to keep on hiking - and I speak from experience. I had serious difficulty going down steep mountain trails. It benefits people who had to be more cautious, and baby their knees.