This was Roger’s response in 2007, taken from a Timezone article:
"It is my goal to eventually fit an overcoil hairspring to all the Series 2 watches if it proves to be the best solution, but we are still monitoring the performance of the watches and we will not fully commit to a spring until we are 110% certain that it is the correct one. But I will only put in a Breguet overcoil if it proves to give better results; it won’t be for looks. Some movements work better with the one or the other; you have to examine it case by case."