Ah! Philatelic investigation! Listen to the rumors, go check them in post offices, eye lots of stamp sheets... opposing to waiting the information being published in the Official Monitor of the French Philately.
Reporter Brian Sinnott came back with sreenshots of the Post & Go automates, as a how-to-use-it for others.
Alway a summary ici, or wait for the monthly "Machin Watch" in Gibbons Stamp Monthly, whose author John M. Deering is lucky (compared to a French author) to put such detailed intels on British definitive postage in such short time (maximum two or three months, due to the dead line of the magazine printing).