We have been looking for a cheap hotel for our short trip to Paris and were adviced to stay in Formule1. I was prepared for shared toilets and showers and for simply furnished rooms.
However, the problem were not these things - the problem for me was the stinky room where there was no possibility to open the window, garbage in the elevator and in the corridors and especially the broken toilets. We stayed there for four nights and neither one day the toilets on our floor were working. And what is the best - all the mess inside was not cleaned once in the time.
It was really nasty, we complained several times and were told to use toilets on the other floors, but the last day we stayed no toilet was working in the whole building.
I don't know about the other Formule1 hotels, maybe they have better conditions. However, Formule1 in Gennevilliers was horrible and I wouldn't recomment it to anybody.