You listen to a sentence and answer. It shows how much you actually catch at natural speed.
I understand it with subtitles but not by ear. Why?
Reading and listening grow separately. To find out whether sentences you know on paper slip past you as sound, the text has to be taken away — which is what this check does.
How many times can I replay it?
You can replay. But a real conversation has no rewind, so what you catch on the first pass is the closer match to your everyday listening.