It shows a small overlay on your left - corner screen to show you your current screen refresh rate.
The app sizes about 10 MB, but if you are worried about the source trust, you can use and run the plain Python script provided.
If you are using The EXE file, then there is only one way to close the overlay.
Go in Task Manager, and search for "Refresh Rate Overlay.exe" in the backgroung processes, and then click on End Task.
If you don't know what to do, just simply restating the PC can do the same.
If you are using the Plain Python file, some Python libraries need to be installed to run the Python file.
[Not the .exe] (Libraries Command file is attached)
Any bug reports and glich complaints are welcomed !