The UCR slingpack is definitely the most utilitarian pack I've ever owned. All of the straps, zippers, handles, pockets, and features seem sturdy and dependable. They'll last for a long time for sure. The main strap is about as comfy as it can get with a slingpack. If you really need it, you can connect the cross-body one to it to better help you distribute the weight where it needs to be on your back. I got the storm colorway, and it's a bit of a darker gray in person, which is good in my opinion. The pictures on the site make it look way brighter than it actually is.
As far as capacity is concerned, I had no trouble fitting a 13 inch notebook in it, surprisngly. I was also able to put a 750mL water bottle in it vertically and still had just enough room on top to zip it up completely. If capacity is ever a problem, you can always take that water bottle, jacket, or whatever and put it on the side or bottom on the outside of the slingpack by tucking it into the compression straps. The MOLLE on the main strap and the back of the pack provides a lot of space to attach additional pouches if you really need to as well. I originally bought the UCR slingpack for the purpose of having a portable EDC pack which can carry all my stuff easily and comfortably. Now I'm thinking that it's useful and capacious enough to replace some of my larger backpacks if I'm using it for traveling.
There aren't many flaws in this pack, but one thing that could be better are the zippers to the main compartment. It's a good thing that they have pulls on them, because it's actually sort of awkward and difficult when trying to zip them up. You're probably going to need two hands every time you do so. It likely has a lot to do with the path of that zipper in general (it has curves in it). If they can figure out how to make that consistently smooth enough to open with one hand, the overall functionality of this pack will shoot through the roof. Also, it should be noted that the UCR slingpack is not waterproof. You can see the two grommets at the bottom which are there to quickly drain any moisture that gets inside. Full waterproofing would probably require taped seams, aquaguard zippers, some sort of DWR on the ouside and changing out the velcro MOLLE to something else. So I can understand why they wouldn't go that route. What I'll probably end up doing is getting a small waterproof backpack cover that fits it well and then just keep that in a pocket so I'm prepared for any unexpected rain that comes my way. 5.11 would do good to make one themselves and include it since it wouldn't really cost much more to make, but again, this would add a massive amount of functionality to the pack.