I feel each book is a good overview of the subject; for in-depth studies you will need a curriculum. I am using them for a good all-around view of subjects I don't plan on covering in depth. mainly Physics, Chemistry, History of Mathematics, and History of Medicine. My son is going to do the Biology book too although he's had a year of Biology already. That is something he seems to enjoy and do well in.
I don't think the briefness of the books have anything to do with the Christian viewpoint. It's just because it's trying to cover all major concepts in a short period of time. However, being that way, if a kid has a short attention span it is easier for them to get through a chapter in these than a large textbook. I am having my son work on 2 books at once for his 'science' class right now.
I started out with 3 of them just to see how they were and dh actually read them first and enjoyed them...but he really likes science stuff. Although he didn't care for Saxon physics when I bought it either.
Tell your dh can if you don't like it after perusing it you can always return it to Amazon. I've done that and Amazon has always been good refunding my money as long as it was within 30 days. I mean, it may not be what you're looking for. Sometimes you just have to touch it, turn the pages, and read for yourself before deciding. That's what happened with us with both Saxon, and the Keys to... series for Math. Although they were reccommended, it just didn't appeal to us after getting them.
Hope that helps.