Perhaps more useful than a rubric is a checklist, so I developed one. I based my checklist on one created by Palm Beach County Schools and Edudemic.com. The checklist addresses both instructional and technical aspects of an app. For simplicity of purchasing, my list favors free apps and apps that do not have in-app purchases.
Using a rubric is a super helpful way to stay on track when evaluating digital tools. It helps guide you and can help see ways in which the digital tool is great and can show where improvements are needed.