Seems well made, as I'd expect from Castelli. Had to laugh at the XL name, though. It is XL compared to other saddle bags in the same way that Castelli XL jerseys are XL compared to most other brands--in other words, not really XL at all.
Packed fairly tightly, i was able to include a road tube, two CO2 canisters with an inflator, two tire irons, a multi tool, and a cloth mask. The bag fits very snuggly under the seat and looks pretty good. For me its size strikes the right balance between what I want to carry and how big of a bag I want under my saddle. If I flat, though, I will have to unpack and then repack the entire thing in order to get the tube out.
Nice design. Castelli panache. Too large for my needs though. Ordered the Castelli mini which is perfect for 2 tubes, 2 CO2 cartridges, and CO2 regulator head. This one can fit all that plus multi-tool and room to spare for ??? Levers, I guess, if you need them. Need to take off bag to access contents, so it's not handy to store goo or anything you will definitely need on the ride.
I'm an ultra cyclist and often ride for 100 miles+ on a given day, so I have to carry "everything" with me. I've been on the hunt for a saddle bag that's small enough to tuck under my saddle but still hold all of my stuff including a minipump. This bag is perfect! I've tried 5-6 other bags and they are either too bulky, too small, not aero, won't hold my minipump.... But this bag checks all the boxes. HIghly recommend.