I've been using this pack as a daily commuter bag for ~3 months across a wide range of weather conditions, and have been pleasantly surprised by its comfort and resiliency. The pack allows adequate airflow to my back on hot, humid days, and the bulky waist strap doesn't cause me undue sweating or irritation. In fact, I thought the waistband was a little obtrusive at first, but I don't even notice it while riding. I've also worn this pack through some intense rainstorms, and the inside of the pack always remains dry. I wouldn't call the material waterproof, but it's very water resistant.
Like other Evoc packs, this comes in different sizes. The "Small" fits my smallish torso fine (Im about 5'5"), though the top and bottom of each shoulder strap can be adjusted to fit much bigger.
This pack has a ridiculous number of storage pouches inside its various pockets. which makes it easy to organize your gear. There's also a small pocket on the underside that holds straps and buckles in case you need to strap gear onto the pack's outside (I use this pouch for spare tubes). My sole gripe with this pack is the single waist belt pocket. All my other hydration packs have two waist pockets, which are useful for stashing snacks, keys, tools, or any other things you might want to access on the fly. This is a very minor point, but it still irritates me.
This is a hefty, high-capacity pack that would be good for long MTB rides or day hikes. It comes with a foam/plastic spine-protector insert, but you can easily remove it if you don't need the body armor. The color options rock, too; I bought the green & yellow model and find its color layout absolutely gorgeous.