The quality of AIM can't be that good if they are free, right?
Only faculty can determine quality for their uses, AIM or not. The AIM guide provides links to collections used by other institutions and are known to curate resources that have been reviewed by faculty. Open publishing models are often similar to those of traditional 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 with various measures of student success when compared to traditional textbooks.