The K&F concepts backpack design is what sold me on this. I love the detachable shoulder straps and the side openings. It's well made and the materials seem very sturdy and strong. I looks like it's actually fairly water resistant. The design is awesome! My problem with it is the size.

This one is listed as being 25 liters in size and expandable. I'm trying to replace an old 13 liter LowePro with something a little larger. I thought 25 liters might be overkill but gave it a try. When I place the two side by side this is actually smaller than my old one! The internal space for camera and lens storage is smaller but a little deeper which doesn't actually help. I have a Canon R50 which is small for my hands so I have a grip attached to it. Trying to find a way to configure the internal dividers just to get a camera and a couple of lenses in there has been a puzzle I haven't been able to figure out. There is just no way to use the space well and get lenses in. How does it calculate to 25 liters? Maximum outside dimensions?

I often keep a 55-210 mm lens on the camera body which in comparison to other kinds of lenses is small but between the lens and the grip there is just no simple way to configure the inside dividers and still have easy access to my other lens. Since I carry a small battery charger, small LED light and other accessories which don't lend themselves to the side pockets the top ends up being a messy dump bin. I'm still trying to work out the backpack because I like it and want it to work but I'm thinking more with each idea that I may have to return it.

Edit:
The question about sizes seems to be the way my LowePro bag from 2009 was measured and advertised vs the way sizes seem to be calculated. When I measured the 13 liter pack and did the math the interior storage space measures out to just about the 13. I used the measurements from the description of this bag and a tape measure I finally understood the 25 liters is based on the maximum outside dimensions and has nothing to do with the amount of usable space inside the backpack. I'm not saying it's false in any way, just a different standard of doing things. It's a great bag and the concept seems wonderful. Saying it's a large capacity bag depends entirely on what it's compared to and the expectations of the customer. The standards used to measure bags now seem to be oriented towards travelers and the restrictions on carry-on bags rather than oriented on a day trip hiker who is not going to be lugging a laptop around. I need to readjust my thinking and be more aware that thinking has changed concerning the target buyer.