Based on the users' reviews of the Hand Stack app, here are three cons and pros: **Cons:** 1. "Disappointing experience. Ads are invasive and often crash the app." (15 words) 2. "Limited functionality. Users are disappointed with the lack of features and customization." (15 words) 3. "Glitches and bugs. Frequent errors make the app frustrating to use." (15 words) **Pros:** 1. "Simple yet effective. Great for basic arithmetic and mental math exercises." (15 words) 2. "Fun and engaging. Interactive animations keep users motivated and entertained." (15 words) 3. "Helpful for kids. Educational and easy to use, great for early math learners." (15 words) Please note that these are summaries of the reviews and might not reflect the opinions of every user.