I just purchased this display arm and am extremely pleased with it. Even though the description says "Up to 20(inch)", I am using it with a 23" LG IPS235V, which is supported perfectly. In fact, I was a bit surprised to find that even though I mounted it on a plain (flat) desk, the arm has enough clearance above its base so that I can fully rotate the display into a vertical orientation. I'm using Mac OS X, and it's simple enough to rotate the desktop orientation within System Preferences such that I can quickly use it in "portrait" mode when I wish (very cool and useful when reading tall/lengthy web pages).
I must say, after reading some of the reviews, I was a bit worried if this LCD Arm would work out for me or not. I couldn't find any clear drawings or descriptions of it's positioning features online. But after receiving it, I am very impressed. It took me less than ten minutes to set the whole thing up and attach my display, and I can easily reposition it in many different ways. It feels very solid, assembled and mounted easily, and it even has a built-in cable guide channel within the arm to keep the desk clutter to a minimum
Sure, this arm does have the limitation that it's base angle cannot be readily changed. There is no hydraulic cylinder in the arm as you might expect on first glance, but hey this Arm only cost $29! Which is an exceptional value in my opinion.
Basically, there are four freely moving axis of revolution on this stand. Three of which (x, y & z-axis) are on the head of the arm (where it attaches to the VESA mounting points on your display) and one at the base (z-axis). The joints at the head seem very sturdy and firmly support my display in every possible position. The firmness of the joints causes them to creak a bit while being repositioned, but I notice that rotating the head along the y-axis (shifting the screen from landscape to portrait orientation) is completely quiet.
The base angle of the arm is also repositionable, but only by removing/installing four socket screws. That repositioning only took me a couple minutes of disassembly and reassembly, but it's a bit unwieldily to do if the monitor is already attached to the Arm. Honestly, once you've set a base angle (display height) that works for you, I'm not sure how necessary it would be to adjust the angle (unless people of vastly different heights are using the same computer). So, that's the tradeoff, and one I gladly accept for the price savings. If you really need that feature, be prepared to spend a lot more money (probably at least $150-200 more) for another display arm that is anywhere as close to as sturdy and functional as this one.