I have picked up the Air Zound not too long ago. There is good and bad.

The good.

It seems louder than the Hornit, I will do a decibel measurement tomorrow to confirm.
Does not need batteries.
Way lighter than the Hornit.
It's cheaper than the Hornit.

The Hornit however is perfect for anyone not requiring a super loud horn, easy to use and has a nice look to it.
I love it for what it is so not putting it down by any means.

The bad, which can be made good.

The mount is a joke compared to mounts of other accessories, but it's cheap. With some no brainer mods, it can be attached better with tie wraps.
The air reservoir (500 ml or 1/2 Liter) is way below capacity needs for the city at 80 psi and a fully open valve for maximum loudness. With some mods, we can fix that issue for cheap, already started.
Cannot be pumped by hand easily, a small electric compressor works perfectly especially if you will follow my mods.
It does not work below -10C
It's bulky.
The sound level control valve is a dinky plastic bar which pinches the hose. I prefer to leave it fully open for maximum loudness and quicker refilling.
More difficult to activate than a Hornit.

I will take pics of my mods when I do them and post pics here, some maybe by tomorrow.