Please correct me if I am wrong but doesn't pitch have something to do with how well one can hear the whistle regardless of decibels. The Fox 40 produces a lot higher pitch than conventional whistles. and from what I have experience is younger people hear the fox 40's a lot better than older people.
I do have to agree that it seem to take a bit more work to get the fox 40s going but it seems the work is well worth the extra effort.