Bart
If you look at the spec page for each tripod you cut thru the sales hype and get a list of features. The features page doesn't really tell you what that particular model has.
This is hard to explain in detail how to get to this page and I can't send you a url since this is all internal to
B&H. Here goes anyhow, if you go to Gitzo tripod legs, then pick one particular model. You will see the description page where you have a chance to add that model to your shopping cart. The Accessory tab (just below the picture of the tripod and its brief description will be selected automatically. You need to select the Specification tab (Your choices will be Accessory, Features, Specification, and Item includes). Then you will see the specific number of leg sections, the material, the closed length, the weight, and a description of the center column or a note that it doesn't have one for that particular model, and more.
You do need a little help with the code words. eg. "ALR" means anti rotation leg couplings. That's what Daniel is describing. G Lock has to do with a new system to tighten the leg twist locks. And both those things are very nice. My older series 3 doesn't have either, but you can see some models that do at HCE. I was there last week and they had the Series 3 equivalent with ALR on display. The catalog HCE has chained to their display is old, so has little or no value on the newer models.
Steve