Unfollowers for Instagram is a well-reviewed app in its category. It surfaces the core data points creators care about: who unfollowed recently, who you follow that ignores you back, and how those numbers move over time. Users download it precisely because it works. The issue is not whether it delivers the data. The issue is how it gets the data, and what that costs you.
To retrieve your follower information, Unfollowers for Instagram needs active access to your Instagram account. That means your login credentials, passed to a third-party service. Instagram does not authorize this. Their Platform Policy explicitly prohibits storing user passwords or impersonating users to access the API. When Instagram detects it (and they do), the account faces action. That can mean a temporary lock, a forced password reset, or in repeat cases, a permanent ban.
WhoUnfollowed was built specifically because this tradeoff is a bad one. Instagram gives every user the right to download their own data under GDPR Article 20. You go to Instagram's settings, request a data export, and Instagram prepares a ZIP file. You upload that ZIP to WhoUnfollowed, and the app parses it locally in your browser. If you upload a second ZIP from a later date, you see the diff: everyone who unfollowed you in that window, timestamped. The file never reaches a server. The app never touches Instagram. There is nothing to flag.