To address your points:
* Competition: The current hotness as far as shaker bottles is only $7 on Amazon [1]
* Watches: Most people don't wear watches anymore. I'm one of the rare people who do, but if I didn't want to wear it, I'd just leave it in my gym locker. Why carry it if I don't need it? Especially if it's an expensive watch.
* Phones: Likewise with my phone. If I'm not listening to music on it, I'm going to store it elsewhere secure. I'm not going to carry it in a sealed compartment in a bottle that I'm setting down a lot (and thus have to keep an eye on).
* Shakes/powders/amino acids: For a lot of these, you're working with 32 oz increments of capacity. Hence why most shaker bottles are 32 oz.
The configurability as far as fluid mix/match is really, really cool, though. Being able to buy parts is attractive (eg. to put together 2 large fluid compartments, one for water, one for electrolytes or something). And at a $10 price point, this becomes more attractive.
The device storage though, seems kinda gimmicky or ancillary.
Don't get me wrong. I'm not necessarily trying to tell you to drop this product. I'm just hitting you with the questions that come to my mind, as a potential consumer. If I didn't care, I wouldn't even have bothered to post :-)
1. http://www.amazon.com/BlenderBottle-Classic-Shaker-Bottle-28...