Al-kitaab is a diffcult book to self study, and somehow an even harder one to work with in class. While it's inefficient, somewhere around book 2 you've aquired enough vocabulary and grammar to speak in fusha, although unless you've really followed through with a dialect for ammiya you're going to need a tutor to help you out. I wouldn't put too much stock in the reviews for the textbook.

Realistically, arabic is difficult, and actually speaking street arabic is frustrating.

Source: Currently doing arabic, spending the month in Jordan on vacation doing an arabic intensive, using al-kitaab in both classroom settings and self study.

Arabic is, however, definitely terrific. I'm definitely going to blow all my vacation days next year to come back again.