For audio which ends at 20kHz its sufficient.
Afraid it is not quite so simple.
With audio amps you can get oscillations from 2MHz to around 6MHz, and with MOSFETs the sky is the limit.
You can also get artifacts at any frequency: x over distortion for example.
Even taking the highest audio frequency of 20KHz, many audio amplifiers respond to 100KHz and higher, which means that 100MHz is only two decades higher. So if you are investigating/designing frequency stability a scope with a high frequency response is essential.
Then there are class D audio power amplifiers, which involve relatively high switching frequencies.
Plus, there is a host of other aspects in audio work especially when you get into the digital audio field.
With scopes of any breed, I have found that the critical factors are frequency response, resolution, low noise, and good triggering, assuming of course that all the fundamentals are in place: reliability, accuracy, ease of use.
You can't always go by paper specifications and, say a Tektronix scope with an equal specification to a lesser make, will have a far superior performance in practice.
A scope may have a stated frequency response but what happens at higher frequencies; with one scope the response may drop like a brick, but with another scope the response may drop gracefully at unit slope- there is a vast difference between the two. Also, some scopes do not even meet their stated frequency response and/or are not flat in their pass band.
Just to make it clear- I am not trashing any scope however humble, and the scopes that I used when an electronics newbee were very humble but still extremely helpful in investigating practical electronics.
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