Twin Zaku Question

[Shinryu]

I was planning on buying Twin Zaku, but there's one thing I'm just a little bit unsure of. The releases that the techniques for it list are Ototon/Fuuton.

Does that mean one is needed, or both? If it does need both, can someone explain the necessity of having Ototon? As far as I can tell those techniques have pretty much nothing to do with sound jutsu.

[Hop]

It would be sounds and wind, I'd say it is unclear using a '/' to describe that, but if you read the description of the technique it says sound AND wind.

[KID GAMBINO.]

It is the manipulation of both Ototon AND Fuuton, at once, so yes, it requires both releases. As for the reasoning for the need for Ototon, this is from Naruto Wikia, which is a pretty reliable resource for Naruto information when needed:

...allowing him to propel a combination of air pressure and sound in various ratios, controlled by his chakra.

Using the air tubes implanted in his arms, Zaku can control air pressure, creating supersonic blasts of air.

[Shinryu]

Supersonic blasts, eh? Blasts that move faster than 750 Miles an hour? Why has no one done the math on this, yet?

[Comatose]

Because according to what we've seen in the anime and manga they are really special supersonic blasts. By that I mean they are supersonic blasts that fire at the speed of like a paintball.

Regardless, no one is taking the description quite as literally as you. It's a just a fluff descriptor.

[yōmi]

^
To add onto this. The speed of sound is much quicker than the speed of anything else unless referring to light.