I actually have one of these. It is probably as loud as the one above, but you can use it as many times as you like, and it never runs out of air.
If I did have one like shown in the previous post, I would be looking for a squeeze bulb to fit to it, instead of having an air supply that runs out.
People are being light hearted about having a truck horn on a bicycle. If you live in S E Asia, where people completely disregard the road rules, sometimes it would be very handy to have a very loud horn. If I can find one that is loud enough and light enough, I may actually put it on my bike.