I wanted a light weight bag I could use as a rucksack or attach to a cycle rack. Its not particularly lightweight (important for aircraft cabin bag weight limits), but it is sturdy and has dedicated rack clips for hooking to a rear pannier. The capacity is large enough to get clothes, shoes, toiletries and a book or two to last a thrifty traveller a week or so. I'd have preferred if the zips could be locked together (one set can, but two other cant) and the underneath flap which hold the rain cover is inelegant and offers poor security. My biggest gripe with the design is that when used in pannier bag mode, the bag is secured through two clips and a hook that are mounted on a flap. This flap is zippered to the main part of the bag, but if the zip should fail (they do, especially if the bag weight is cantilevered as in this case), then the main part of the bag will fall outwards and towards the ground will still remaining attached to the pannier through the clips. The zippered part is attached (hinge) at the bottom, so the bag will not fall off completely from the cycle, but will hit the ground and be pulled towards the rear wheel. If the zip should fail, then a better fail safe solution would be to have the "hinge" at the top.
To avoid the risk of zipper failure, you may be able to attach the bag to the top of the rack and lay it flat, or use it as a normal pannier bag with a compression strap around the bag just under the clips, reducing the strain on the zip