Based on the users' reviews of the app Zero21, here are the conclusions: **Pros:** 1. Users praise the app's simplicity and ease of use, saying it's easy to navigate. 2. Many appreciate the game's engaging gameplay, finding it challenging yet fun. 3. Some commend the app's stability, reporting few or no bugs and crashes. **Cons:** 1. Some users complain about the app's in-app purchases, calling them "aggressive" and "pushy". 2. A few reviewers find the game's graphics and sound effects to be lacking in quality. 3. Some users experienced difficulties with lag and slow loading times, disrupting gameplay. Note: The conclusions are based on my analysis of the user reviews available on the Google Play Store at the time of my knowledge cutoff.