Using the app is very simple. Just search by channel name and select it from the list. In addition to daily, monthly, and annual dollar earnings estimates, total subscribers, total views, number of videos posted, and total comments are also displayed. You can also change the eCPM used in the calculation in the "Settings" menu.
It is important to clarify that all information used in the app is public and made available by Youtube itself.
Now you can verify, how many times you want, either how much your prefered youtuber earns or your concurrents channels. Enjoy it!