I got the chance to try out the ShredBak for several hours at the Backcountry Base Camp (the on-snow outdoor session of the Outdoor Retailer Winter Show) while demoing skis and snowshoes. This included riding the lift (which I hate), skiing a couple runs (limited by the vendors to one run on each pair of skis, because of the number of people wanting demos), and running (literally) up, down, and across some steep slopes on snowshoes. I did have to make do with water, rather than my favorite hydration mix (that's what they filled the bladder with, and I didn't have the mix with me).

The vest was extremely comfortable, so much so that I would forget I had it on with its 2 liters of water (less each time I thought about keeping my hydration up and drank a bit). The compression inner vest was a bit on the tight side, but it kept the water from bouncing around and kept it close to my back. I wore my pack for part of the time, though most of the time I left the pack at the Camelbak booth (as hostage for the demo vest - there's another story there, for a later time). This proved more comfortable than my usual winter trick of wearing a Camelbak Classic under my jacket and pack.

It appears that you do need to be aware of one potential problem that you could ignore with the old trick of the Camelbak under the jacket - Some people have the habit of blowing air back down the tube, since the area that remains vulnerable to icing for most people who leave their jacket open is around the bite valve and upper tube. Some blow the air all the way into the bladder. This makes the bladder firmly inflated, which is not a problem if you aren't wearing a pack, but can be an uncomfortable lump under a heavy pack. The trick here is to only blow the air a few inches down, so the water is in the warm area under your armpit (run the hose under your arm, not over your shoulder where it will sit under the pack strap). Yes, blowing it all the way back and hearing the bubbling gives reassurance that you only have air in the tube. But you don't really need to have the whole tube evacuated of water.

You can wear the inner compression vest by itself. The outer vest is intended as a mid-layer and seems adequate for that (though the day was a bit on the warm side for the Wasatch in winter). Certainly an interesting solution to an age-old problem with hydration packs.