I've noticed a few of the pro's in triathlon using a larger rear bottle mount on the seat posts of canyon speedmax's, Sam Laidlows: https://www.instagram.com/p/CxQ37VKProf/ and Chelsea Sodaro had it on at the weekend too. Seen a few others have them.
I've messaged Canyon but they couldn't point me toward who makes them.
Does anyone know the benefits other than looking cool and know anyone who does make them? I've tried to search google but either its top secret or I'm rubbish at putting searches together.