This is an absolutely superb edition! I'm just dropping by to give it a plug. For some reason, I can't find it anywhere on Amazon by searching for "Montaigne French Edition," so I had to resort to an ISBN search.
What you're looking at is all of Montaigne's essays, in French, in one volume. There are many extras: introductory essays, footnotes, etc. All the Latin and Greek is translated into French. There is not a single word of English anywhere in the book.
The most important thing you need to know is that in this edition fixes up Montaigne's spelling to be that of current French. It doesn't fix his diction, though, so sometimes you are told about that. But if you've ever peered into unretouched Montaigne, it's a bit like looking at unretouched Chaucer, with the wacky spellings and all. No, the spellings, contractions, and punctuations have all been rendered in modern French, just not his vocabulary and grammar.
I know of a better edition of Montaigne's essays, but not a single volume. (The three-volume job I know retains Montaigne's original spellings.)
The book is larger than a normal paperback, but not oversized. The pages are very thin, though: about the thickness of those used in the Norton anthologies.
The overall editor was Jean Ceard. The publisher is "La Pochotheque." The ISBN is 2253132721.