I've got a Shiv with that cage and bottle. For normal training I use a round bottle and cage because I've lost my bottle crossing over a sidewalk with one of those 2" lip curbs. I only use the aero bottle and cage for TT's. and I use it specifically because the bike is more aero with that bottle and cage than without. I don't drink during TT's, but keep just a bit of water in the bottle so I can have a sip before the start and after I finish without having to go to my car. My rule was always to never drink during TT's and "back in the day" took my bottles and cages off before a TT (Way before we had aero tubes and bottles). Then one day I did a 10 mile TT when it was over 100 degrees and thought I was going to die. I did a second one that day, put a bottle on and drank or poured the whole thing in 22 minutes or so.
For Sagan's case my first thought was along the lines of others here, "why do you need to drink in a 35' TT". However, they don't do their TT's early in the morning like most of us do. That TT started at around 3 or 4pm. I know that it's been warm, so it was probably easily 80-90 degrees for their TT. That makes a difference. Also, they need to think a lot more about staying ahead of the hydration and feeding curve because they raced 100+ miles the day before and will race 100+ miles the next day. And the day after that, etc. Also, in a TTT there is no penalty for sitting up a bit to take a drink when you're at the back, so why not?
As for the ability of that bottle cage to hold, 1 it's pretty weak when compared to something like an Arundel cage and 2, it's only holding the bottle from the sides compared to wrapping around the bottle like a round bottle and cage. Go pick up a 20 lb barbell at the gym in each hand. Wrap around the barbell with one hand and squeeze the barbell from the sides only with the other. That's the difference.
Kevin http://kevinmetcalfe.dreamhosters.com My Strava