These are my reasons, in order, for trying rear-mounted bottles out...
There is some trauma in my left arm that means it's weaker - I can't reach down and grab a bottle with my left anyway but reaching down into the frame with my right means more weight on my left and some inevitable instability.
I'd like the triangle to look cleaner.
Bottles at the back are more aero (actually this is probably least important - I'm not that fit and it's an Alloy Synapse, not an aggressive position balls out racing machine where I suspect aero might matter more)
The rails on this saddle are really odd, not sure many, if any, of those would work out of the box. And, aesthetically, I don't like seatpost mounts. It's bad enough having to velcro a strap round it for a small saddle pack..
I've just enquired about a small piece of nylon that I'm thinking I might be able to drill a couple of holes in, file out a couple of grooves for the rails and use that as the mounting plate for the double Minoura mount. A rethink on 1 litre bottles might be in order to prevent bumpy road ejection.