I purchased this frame pack for larger excursions. Have not used it yet, but it does fit my frame perfectly. I have the frame pack in small which is on my gravelallaround bike all the time. I use the small pack as it holds all the stuff I need on most rides easily and leaves a bit more room to pull out my front water bottle. These packs are stylish, well made, and light. The small frame pack weighs less than any seat bag I know of and holds more. It also means a tail light can go anywhere.
I bought this for my cross bike as I had limited storage riding Canada to Florida with just rear panniers. I use it for training rides now. I put a second one on my disc trucker, took off the front racks and will do the CDT in August with large rear panniers, apidura frame pack and small handlebar rack. I ride an XL frame.
We purchased this for our recumbent tandem to carry some tools and a large external battery to power an iPhone for all day navigation. It has held up well. It is water resistant, but an all day rain will get some moisture inside. Thus, anything that must stay dry should be in a plastic bag as well.
I ride approximately on average 95 miles per-week. I use the pack to carry my pump, rain jacket, spare tire and repair kit and a snack. I know it sounds like a lot of stuff, but it all fits well with plenty of room for my legs and even for my tire irons (spoons) ,-)
The pack keeps its shape, as long as you do not over extend the sides, it fits well and protects your stuff. It beats wearing a back-pack. The sales representative was very knowable and helped me pick out the right size for my 54 cm frame.