I'm a HS teacher who uses the AR program, and find this useful both when shopping for used books, and when labeling book levels in the classroom. I find it is accurate on about 9 out of every 10 books - so please make sure you check the title and author when the result comes up, as sometimes it will give you a book with the same title by a different author, or occasionally something completely inaccurate. (I think this might be an issue with ISBNs, though, as they are often book fair titles, books from small publishers, or really old books when this occurs - I'm not sure that the app can fix that, just a word of caution for teachers trying to save time.)
I am taking one star off because I have a few issues with the interface: first, when I open the app, I have to click "scan barcode" to scan a barcode. Since that's the literal purpose of this app, I think it would make more sense if the scanner was the default when you opened the app. Second, if I've just scanned one book and am now ready to scan the next one, I have to hit two buttons in two different areas of the screen to make the barcode appear - first "back" in the top left, and then "scan barcode" in the bottom center. This slows me down and makes it a little awkward to use the phone with one hand while I'm holding books in the other. Finally, when I click the icon to manually search ARBookFind, it defaults to advanced search rather than quick search, which means it takes a much longer time to input the information - rather than just typing in title and author in one box, I have to input each detail in the correct box, or manually click "quick search" to simplify the process.
Overall, this app is already 100% worth $2 if you are a teacher working on an AR-friendly classroom library - but if the developers would fix those three usability issues, then it would be absolutely perfect. I imagine it would be helpful for school media specialists as well.