I bought this in preparation for my first 30k trail run because it was a no-cup event. I went with this lumbar pack due to price and also because I already own a backpack hydration system, but it leaves my shoulders sore after long runs (besides the vest- and backpack-type systems I didn't want to go with a handheld because it throws off my rhythm). So, I'm happy to say, I'm very pleased with this purchase: having two 10oz bottles offered me the right amount of liquid between aid stations, and the front pocket fit my iPhone 6 (I had to remove my 6's protective case to fit it in the front pocket, but it fit nonetheless--a 6+ would not fit in the front pocket.)
At the stating line then I had my waist pack loaded with 10oz of water, 10oz of nuun, my race bib conveniently secured to my side, two mini Larabars, my car key carabiner'd to the bungie cord, and a mini ziplock with chocolate-covered espresso beans. All of this snugly cinched up on my waist, did wonders during the run: no chaffing, no bouncing, no agitation. When I needed a snack I easily slid the back section towards the front, removed my snack, ate, stuffed the wrapper in the velcroed pocket, and slid the bottle/pocket section back behind me again with my phone in front, all without breaking stride.
If I had one complaint it would be that the fasteners for attaching the race bib move freely, so unless you safety pin them to the waist belt (which would hamper your ability to slide stuff around to access while running), the race bib tends to fold so that left and right fasteners walk to meet each other leaving the bib folded in half. Now, this is by far not that big of a deal and can be avoided altogether by shouting your race number to the guy with the clipboard, but still, it is a criticism, and probably my only criticism given the solid construction and ease of use that this lightweight waist pack offers. Nice work UD, you guys got this one dialed!