If you enjoy seeing where you're going when grabbing a much needed swig of hydration mid-stride over treacherous terrain, heading out on a long run as light as possible, and knowing that your bottle is securely in your hand at the end of an exhausting training session then this bottle is for you. A little extra bulk means you have plenty to hold onto and for it to hold on to you. The wide strap and breathable mesh help the bottle stay securely in place, even when you're sweating like a fool and can barely make a fist from that grueling 2,000ft climb. The angled neck means the less you have to strain to get your hydration, and also allows you to keep your eye on the terrain and not the sky. The pocket is perfect for energy gels, keys, even a phone if that's your style.
I was recently given a Nathan UD at a race and gave it away to another racer because I love my UltrAspire that much.