When I walk with my wife, I've only twice heard someone with a bell. Both were electronically generated. One was loud enough to hear from a distance and was the easily identifiable "tl'ing, t'ling" that I'd think we'd all identify as a bicycle bell. The other was very low frequency and not so loud. It was almost a horn sound that wasn't easily identifiable as to what it was and the direction it was in relation to me. The bike was passing before my brain told me that an approaching bicycle might be the source of that sound.

So if you are going to use one for the purpose of alerting pedestrians and others, the classic bicycle bell sound it probably the better choice IMO. Mainly because more people will recognize it for what it is.. If you just want to scare the pants off others, then I guess anything is okay. But don't gripe if I accidentally knock you off your bike as I turn from being startled and move from my line of walking to your line of cycling.

No matter what, I and other walkers, joggers and etc, do appreciate cyclist letting us know you are about to pass. It let's me know not to point at something on the other side of the trail. And I have almost clothes lined several cyclist that way.