I bought a pack of three of them when they were on sale at one of the online vendors.
My main purpose was installing one in a Chichago and North Western push-pull cab car where it served a perfect solution for this application.
I have a bell, horn and air conditioner compressor sound, plus air brake and wheel squeal sounds, directional headlight, marker light, gyra light and roof-top rotary beacon all wired in to it. I forget now where I mounted the speaker but it was before the proliferation of the tiny cube speakers.
Another one was mounted in a mechanical refrigerator car. It cycles the engine sound on or off at random. I have the volume very low but occasionally a visitor will hear it and comment on the sounds.
The third is mounted in a Budd Great Dome car. These cars had an additional diesel engine for the air conditioner. Again, the volume is very low but if you pay attention to the passing train you can hear it.
The squeal sounds are a nice touch and I have them set up to occur at a not too frequent cycle. If you hit the emergency brake you can hear the brake line exhaust the air.
I have fun with them, that's what its all about 
Regards, Ed