My husband and I have done nine self-guided walking tours in Europe over the past 12 years... number 10 coming up this summer. Three of those walks have been in France. I've also done lots of hiking in the Luberon area of Provence and know quite a bit about walking in that area.
I'm obviously very positive about the idea of a self-guided walking vacation. It's a great way to experience the countryside and get some exercise too. And I think if you're coming from abroad, it makes sense to book the walk through a company that knows the area and can handle the logistics for you.
That said, I've never heard of this company. This isn't the type of tour that Trip Advisor collects reviews on, so that's not surprising you can't find much. I would want to be sure that the company you're booking with is actually the one who is handling the actual arrangements, not a company that's just a re-seller of someone else's tour (which only adds to the cost and not necessarily anything to the quality of the tour). Also, I couldn't seem to find the actual itinerary for their Provence walk. That would be important to me.
You could always write and ask them some more specific questions. Provence is a great area for walking, and you'd have a variety of options for providers. I'd suggest going in May, early June, September or early October.
Kathy