I got this pack specifically for trail runs, and after trying it out this past weekend, I am very pleased. The slim profile is the perfect size for me and I wouldn't want any more volume on a run. I like the reservoir opening, though I understand previous reviewers' concerns about drying and cleaning. It just takes a little creativity to figure out how to prop the opening wide enough for air flow. I laughed when I saw others having the same experience trying to figure out how to open it the first time. It took about 6 seconds of googling to sort it out, though, so not sure why the negativity. Overall, I love it.