It holds a lot of stuff without having to cram it in. Can carry tire levers, tubes, multi-tool, cash, ID and more and when needed doesnt have to be pried out. Clicks on and off when you need to put bike on a stand. It is waterproof. The attachment to the seat rails seems very sturdy unlike a previous model by Fizik which eventually broke. So far, a great seat bag.
Small enough not to be cumbersome yet large enough to store all road necessities in a neat waterproof saddle bag which we can easily interchange with other Ortlieb larger size saddle bags thanks to the smart clip system.
I like everything about this bag! Small enough to fit perfectly under my saddle, but still enough room for 2 tubes (for a 30mm tire), tire levers, hand sanitizer (never thought I would write that 5 months ago), thin wallet and snacks.
Waterproof and lightweight are also a big plus.
What can I say? This thing is great. Yes, it is a bag and it holds stuff. It's also waterproof, super easy to open, and also to take off the bike. I own three for my bikes. The one downer is that the material breaks down where it is folded after fifteen years or so, but that's a great lifespan for a bag I think.
large enough for complete kit including tube but small enough to be tucked under saddle. No hook and loop closures is great as shorts do not get that scuffed look when brushing against the seat bag. Use internal bags to group items as you may find items clanking if left loose. For century rides I tend to carry several items which are unnecessary for shorter rides but leave bag packed for either type of ride.