An alternative possibility is that a rideshare company sees that Alice always takes the price that's offered so Alice receives the standard price, whereas Bob is price-sensitive so he receives personalized discounts on rides until the prices reach the amount that he's willing to pay.
That can work for two apps but it's tedious once there are three or more. You'd also need to swipe back and forth between apps to find the corresponding prices for each ride type (Wait & Save, Standard, Comfort, etc.), whereas this app groups together the prices for each ride type across providers.
That's a valid concern but I think it's unlikely. No one's account has been locked for using this app. Rideshare companies take a large cut of the ride fare, so locking user accounts for using third-party apps is against their incentives. It's more likely that they would try to prevent this app from working, rather than targeting users of the app.
App Review didn't object to that. There are various apps on the App Store today that rely on reverse engineering, such as unified messaging apps, alternative rideshare price comparison apps, and driver-side rideshare aggregators.