Interesting, I worked through an older edition last year and I wasn't aware they had updated it. I noticed they make available a preview pdf of the newer edition that includes lesson 1 and lesson 100:
https://monachat.assimil.online/extrait ... xtrait.pdfIf those 2 lessons are a respresentative sample, they've rewritten the dialogs. Were you planning on getting the audio files as well? Note that the audio can be very slow during the first 50 or so lessons, so much so that some people preprocess it in Audacity or a similar tool to speed it up.
I ended up having mixed feelings about Assimil Spanish after I worked through it. At least in my edition of the book, I liked the grammar explanations, but it was challenging for me to come up with a study routine for the material that was effective and engaging. I felt like I got more out of other resources including Language Transfer, Pimsleur and (later) Platiquemos / FSI. My takeaway was that Assimil is great for experienced language learners who have used it to learn other languages but (depending on your learning style) there may be better options available, particularly for languages that are as popular as Spanish.