I was writing a review on this, the big 23l Super C (not the Barley) and got carried away so I thought I'd post here.
I had to work through Ortlieb pannier and Tubus rack ownership etc and buy one of these as an experiment in order to get here mentally. I thought these lacked structure and rigidity but that is their strength and probably the reason Ortlieb don't make them. The slight floppiness and looseness makes them stuffable, expandable, reducible and destresses the mountings and absorbs some road shock. This movement is not noticeable when riding.
They are the simple solution from simpler times and still relevant today because the cap type lid and super c catches address the functional and ergonomic drawbacks of the flappy lid and buckled originals and the cotton duck, unexpectedly, just feels so nice.
I made a cardboard cross section template of the bag to check clearance over the rear wheel and the real thing actually took up less room when fitted. Thorn 26" wheels also help in this area.
I hang mine from Brooks saddle loops and strap it to the seat post in the traditional manner which is quick light and simple. Fitted like this there are many advantages over a pannier and almost no drawbacks. Yes, it touches the back of my leg on the downstroke and I was concerned about this prior to buying but in reality it is not an issue as it just touches but does not rub or slide to irritate and is bizarrely comforting! The advantage over a pannier : no rack (weight, rust, expense, seized or loosening fasteners and metal fatigue: all gone!). Sits higher up so stays cleaner and easier access and no heel clearance issues. Sits further forward (ahead of rear spindle!) so no frame whipping when honking up hills. Yes it "looks" like it would raise the bike centre of gravity but it doesn't feel like that in practice. I am also convined it has less aero drag than one big pannier.
Weight! 900 odd grammes to carry 23 litres with no additional hardware. This is NOT heavy in my book. One 20l pannier is a little bit heavier before you factor in the rack. Or look at it like this, it's only 50% heavier than a Barley saddle bag whilst having almost three times the volume.
I think this bag hits a sweet spot on the cost, weight, volume, durability and ease of use trade off.
Happy days indeed,
Ian