Q. The quality of AIM can't be that good if they are free, right?
Only faculty can determine if a book is good, AIM or not. The repositories listed in the AIM guide are known to curate quality resources that have reviews by faculty. Many of the open publishing models are more stringent than some print publishers. Many open educational texts have been written by leaders in their fields, are peer-reviewed, and professionally designed. Ultimately, you'll need to review the materials and determine if they meet your needs to support student learning outcomes. Studies have found that AIM are either equally as or more effective than traditional textbooks.