I purchased this seat bag to replace a Blackburn bag I've used for years. I shopped other brands but decided on buying a Blackburn bag again. I went with the large size, its a bit bigger than I need but still not too large. The water resistant material, practical inner design and great zipper all are nice features. This bag also secures tightly - no worries of it becoming loose. In use for a couple months, no complaints. Great looking bag as well.
Overall its an excellent bag. Quality is top-notch and it looks itll last a long time. Capacity is ample - I can put all my tools, snacks, phone, jacket and theres still room to spare. One suggestion is to replace the velcro straps with Voile straps, especially the strap goes around the head tube.
These bags are of very good quality and very functional. Easy to adjust to your racks and the ability to move foward or backward when mounting. I've used them on a couple of bike camping trips with no issues what so ever.
Better yet, Western Bike Works always has great sales and excellent customer service.