I have to concur with Misius. First, the initiative is definitely laudable! I love the idea to teach Latin with engaging conversations, which the students easily can relate to. From what I have seen, they are very well written in this regard. The recordings are excellent too!
However, to be frank, only in the part that Misius cited, I have some issues with the language itself, which taken together would make me reluctant to use the text with my students.
In "Caesar et bella sua erant..." there is indubitably a grammatical error: as you know, "suus" generally is placed in a grammatically dependent phrase/clause and refers back to a subject (I'm glancing over some difficulties here, of course). Thus, you can say, e.g., "Caesar narravit de bellis suis". However, with the conjunction "et", the two conjuncted phrases are on equal foot: "Caesar et bella sua" can only mean something like "Caesar and their own wars", i.e., the wars belonged to the wars themselves: a very strange construction. Here it must be "Caesar et bella eius". (I might also add that I find it odd to use this as a subject -- Caesar and his wars, they "were"... what exactly? I would propose "(Schola) erat/fuit de Caesare et (de) bellis eius".)
I did not understand the meaning of "Ita obstupefactus sum" until I found and read the English translation ("I am so surprised"). With "ita", I would expect some kind of comparison or consecutive clause (ita ... ut); correct me if I'm wrong (which certainly may be the case), but I don't think "ita" can be used in an absolute, strengthening sense like this, except possibly after negations. Consider "valde".
"Plurimi hominum", while not really an error, seems like a calque of the English "most people". But there really is no reason to add "hominum" here. In the classical corpus, "plurimi" alone is common, but not "plurimi hominum". Another possible Anglicism is found in "valde delectantes existimant": I certainly don't want to appear like some kind of self professed arbiter elegantiae, but, personally, I would be wary of using "delectantes" as an adjective like this. (The verb "(me) delectat" can be translated as "is interesting (to me)", but you wouldn't say *"est delectans".)
While I'm at it, from all that I have found about the Latin word "classis", it can only refer to a group of students (them having been "classified" in some way); it is then strange to use it for "lesson", especially as there are far better terms available, such "sessio" (fairly generic term), maybe "(prae)lectio" if applicable, or, my favourite, "schola".
I sincerely hope this does not come across as overly critical: I don't want to rain on the parade, but at the same time, I don't think anyone benefits from ignoring possible problems out of misdirected courtesy. There certainly are many good things about this book, and it is obvious that quite a lot of effort has been put into it.