I have those at my high school, and a couple of EST genesis horn strobes in a small part of the building. The speaker strobes I hear more than the horn strobes which probably explains why the horn strobes were meant to cover that small area and be drowned out by the speaker strobes. (Edit 6/18/2025: the horn strobes are just strobes.)
Pretty cool! Edwards made many different versions of the Genesis Speaker Strobe and it looks like this one uses letters to indicate the candela; C would mean 30CD or 115CD. This letter indicator reminds me of the older 4903 series devices that use a colored shape to indicate the candela.