BTA, the integrated can get hot, especially if you have a black frame.

Why wouldnt you use both? I dont use any frame bottles and only have BTA and BTS systems for carrying hydration.

In an either/or situation, I prefer the BTA. It allows me to drink on the go in aero via a straw. I grab the bottle from my BSH to fill my BTA in two bottle events.

BTA first. It's easier to access and (if done right) improved aerodynamics. Also, less chance of launching a bottle. I use BTA for water and BTS for a calorie bottle (since you access that less often).

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)