I purchased both size bags and found them far more durable than any product. Years of traveling checked at airports, hiking, bike touring!!! After almost a year and a serious bicycle accident I had a small hole where most materials would she'd against the pavement. I patched it with a tough reflective sticker and it's as good as new. All I know is that it's the only back packs I'll ever need, recommend and ever purchase again.
Bag is spacious: fits all I need for gym (a towel, and sportswear including shoes). It has nice set of compartments. I am satisfied with the quality and the looks of it. The only downside is that the center of mass of the bag is quite far from my back which makes it move a bit more than I would like. Otherwise - great so far.