I was going to post a review on the Galeforce blaster in the community forum. I had my Galeforce for three weeks now and pretty much ready to post my impression, but you beat me to it, so I'll report what I got here.
If you have to get one horn only, get an Airzound. No second guessing. Here is what I experience. The Galforce is loud indoor. Using an Iphone db app, it is louder than an airzound by couple of Db, but outdoor is a different world. The higher pitch and freq of the Airzound is way way better. It is easier to pin point the location of the blast. While the blaster is not loud outdoor and seem to just spread out the sound with little distinction. The blaster is better if say you are on a MUP or sidewalk and want the pedestrian in front of ya to get out of the way without blowing out their ear drum or their baby eardrum in the stroller with the Airzound. I kept mine on the bike just for that use only and as backup if I ran out of air, which is no longer an issue with the bigger bottle.
9v is Ok. It does not last long and battery dies faster. 12v last longer but not any louder even with a SLA at 12v in hoping it was a current thing. 15v is better and more louder but still not enough for street use. I took the chance and voided the warranty by running double 9v in series for 18v. It is much louder than the 9v setup, yet the freq and tone is nowhere near as effective as the Airzound. So far I ran two weeks with the 18v setup with no damage to the voice coil yet......
Get an Airzound first for traffic than a Galeforce Blaster for Pedestrian for thing like trail use. I have not tried the other Galeforce Siren which has the siren tone and the Blaster tone, but from what I heard, that tone sound more like a car alarm than a police siren and we know how much most people ignore car alarm tone.