It’s a classic ridge walk, fairly airy in places so you’ll need a head for heights. There are some new chains on one of the steeper sections. Not on all of them though, there is still a section which is fairly scetchy that has a couple of fresh bolts in it. Great if you have a rope, not so usefull otherwise!
It’s important not to set off if you think the going will be wet on top. The path is clay, if it’s wet it’ll clog your boots up and that could make things even trickier, a slip on some sections doesn’t bear thinking about.
Ideally you would leave a car at the Col d’Encrenaz, then park at Foron. Leave Foron and finish at the Col d’Encrenaz 6 hrs? later. Otherwise you are either left with having to complete the circuit on 2.5km on road or taking a direct line from the Col de la Bas back to Foron over the slopes of the Pointe du Replan, there is no path to speak of here and it’s quite hard going.
The day I did it there was a cold breeze blowing over the ridge. It had been dry for 5 days which was just sufficient for the October sun to dry the route out.