I am not a professional by any means, but I use an oscilloscope frequently when building guitar effects pedals. Being able to see a fuzz pedal's "clip" is extremely useful.

Phase metering is quite important as quite a lot of audio gear can sum stereo signals to mono, which can lead to undesirable frequency cancellation and loss of signal. FFT is handy for all sorts of things, eg a high-frequency spike might indicate a blown cap in a filtering circuit.

I would not suggest that this watch replaces a proper oscilloscope for lab work. For that matter, the great majority of problems are more easily diagnosed with a computer and some decent audio editing software, which will have things like frequency plotting and phase metering built in. But it looks very handy for location work, eg there have been times when I've had to repair a cracked solder joint in a shotgun microphone in the middle of nowhere, and had no way of testing the gear I was working on before putting it back into service.

The one thing that I don't see on it that would be enormously useful (but also power hungry) is a backlight. It seems like you would end up needing to point a flashlight at it in many situations.