I have the glidecam 2000Pro with the arm brace. It carries a PD-150 which comes to a total of about 7 pounds with the counter weights added. If you have a heavy camera you will need the arm brace. I got mine on ebay from a glidecam distributer.
Pros: Very smooth shots running up and down stairs or any where once you get it corectly balanced which is not easy. Also can be used as a mono pod
Cons: Can only shoot with it for limited time before your arm and back start to cramp
The 4000Pro is too heavy from what I hear and is not recommended
P.S. The key to balancing it is the counter weights must at least equal the weight of your camera.
We have the Hollywood Light which is as good as any of the Steadicam kind of gizmos. They really should be the tool of last resort.
As as been said getting any of them setup correctly has far more impact than the differences in design. The second biggest thing is knowing how to use it. If you know how to walk the walk and the rig is setup properly then you can get excellent results with any of them. Ignore either of those points and you can end up making things worse. That's why guys make their living doing nothing else. Not so bad with a DV camera but with a 35mm rig at arms length you need to be FIT.
So my suggestion, if there's anyway you can get the shot without using one then that's the way to do it. Steadycam shots are not repeatable is another issue to consider, dolly shots are and there's some pretty neat dollies around today. We have the Spider Dolly from Losmandy and it's an excellent piece of gear.
Bungee cord a cross piece onto a monopod, add two 3-pound ankle weights onto the crossbar, put your camera on wide angle and auto focus, and away you go!
Or, just have someone push you around in a wheelchair while shooting.
I built that one myself for about the exact amount believe it or not! It works great and I have used it many times, particularly when I have to track people in motion. You are able to get in close and stay with the action. Really love to work with that thing.
....or just fix a weight to the bottom of your tripod for and even easier solution. Works fine for normal height shooting and you can use the pan arm to control sideways movement.
I used the $14 plans as well. I used a very heavy guage PVC pipe with thread ends in place of the steel pipe in the plans. Home Depot had the right lengths and all the fittings I needed. I already had the weight so it cost me about $9.00 total. I use it quite a bit. I use it to get odd/weird angles as well.