Based on the logic of the series, a sound fruit could potentially be awful. Given that light travels roughly 1 million times faster than sound in air and Kizaru's attacks can be dodged/blocked, then a sound fruit should send out vibrations that are, by comparison, in slow-motion. Even if you disregard that, there are quite a few characters than can affect the air around them and thus, defend against sound rather easily. Zoro, for example, has an attack where he practically causes a tornado. Luffy has his balloon thingy (assuming that he can blow that hard), Nami can produce warm air to bend the sound waves away from her etc.
Light travels ridiculously fast. Sure,
But I'm sure you know that the speed of Sound is serious too right?
I don't think even the Logic of the series would prevent the Speed of Sound fruit from being very fast.
Also, warm air doesn't bend sound away. Tornado's can, but the temperature required for Sound to not travel is ridiculously high.
So Nami is dead if someone with the speed of sound gets behind her at insane speed and lands a hit like how Kizaru lands his kicks.
The Speed of Sound is too fast for a human to react to. (One Piece logic challenges this I know lol).
But Light can only be beat by Vacuum (Lack of air), Tornado's,
In addition, although Kizaru can be blocked, a lot of the time, his attacks work. Kizaru's power is ridiculous and he is occasionally blocked and amongst the most powerful we've seen the series as he was someone who could fight Whitebeard and he smiled casually throughout.
Sound is hundreds of times faster than anything elasticated rubber can achieve.
Its 343.2 m per second. Speed of Light being 299 792 458 m per second so yeah Kizaru is incomparably faster, but Speed of Sound is potentially the second fastest in the series.
Now Kizaru can cover this amount of meters in one footstep. He could cover this amount of meters every few steps in theory.
So a Sound Logia would be able to do 343 m per footstep. That's a over a kilometre in 3 seconds.
So unless you see Nami, Usopp, In fact, most characters reacting to a man who covers over a kilometer in 3 seconds outside of the Haki users who are able to take on Kizaru I think the Sound Logia is a serious fruit.
Kizaru can only be harmed by Haki users. He wipes the floor with anybody without Haki.
It would be the same for the Sound Logia. The Speed of Sound is faster than any speed Luffy can achieve.