it's probably faster and easier to drink m from, especially on a fixie
Absolutely this. I used a bottle mounted to my saddle in a 50 earlier this year, I almost had to stop to stick the bottle back in. I probably won't buy a camelback, but I definitely won't use the bottle cage saddle mount again.
Take it back, buy a camelback bladder and shove it down your skinsuit, it's probably faster and easier to drink m from, especially on a fixie