I found the XLAB after tiring of other seat cages that ejected my bottles like depth charges when I hit dips going through intersections. Riding in Arizona, we can easily drink 60 ounces of water on a 30 mile ride in summer, and this is a great way to take an extra bottle, including insulated Camelbak Podium 21s, which fit. I like the tight fit to keep my extra bottle in place over bumps. Regular uninsulated bottles fit a little less snugly - but still pretty snug. Relatively slimmer insulated bottles like the Podium 21 is very tight, but work. I also have a Speedfil 40 oz. tank system for primary drinking while pedaling. I use the XLAB Aero to carry Heed electrolyte replacement to drink at stoplights, or on a shorter/hotter ride, just water to dump on my head. The seat bag part of this rig holds a surprising amount of stuff, although an extra tube is very tight if you have many other tools. The hardware is very sturdy and adjusts to give you a range of angle and depth options. Once on, it's solid as a rock. Nothing rattling or wobbling. Assembly seemed intuitive. If I had one gripe (let's call it a suggestion, more accurately), is that a tab or loop for a rear light would be a nice addition. For technical comparison, I have this on a 54" Cervelo S1 (aero seat post), with a Cobb Delta M saddle.
This is an amazing bit of kit. Topeak thought of everything, to include an included headset spacer and an integrated work stand. It takes about 20 minutes to pack, but I am getting faster as I get some more reps. I traveled with it and the bike arrived in perfect condition. The orientation of the stand is really convenient to push through airports and on mass transportation. Even the TSA guy commented on how slick it was. Highly recommend this product.