Ergon backpacks (does anyone use one?)
 

I was looking at the Ergon backpacks (BC3:http://www.ergon-bike.com/us/en/product/bc3 ). They're made for bikers: provide airflow to the back, can hold a 3L water bladder, put like 80% of the weight on your hips instead of shoulders (supposedly), and have a ball-and-socket joint that keeps the backpack straight up even when your shoulders tilt.

I've found plenty of reviews where people are saying they're great, but none from people on tours. I know almost no one tours with a backpack, but there are a few crazy people out there, and so I was wondering if anyone could say whether I would die trying to use this.

It's extremely pricy for a backpack, so I'd really rather not end up shipping it home in my first few days...