Clear, concise, love the uncluttered nature of the interface. Great interactive relevant 3D models with each entry, and helpful links and references throughout the text, without trying to stuff too much info on each page. Quizzes helpful. Can browse the material at your own pace, and in your own order. Organization of entries logical and easy to follow. Developer highly responsive to communication, and attentive to resolving issues. Highly recommend this app. FYI, I have the Gold level version.