difference between a quantum and an 580EXII?

[unclened]

i've seen a lot of people use the quantum set of flashes and I understand that they are more powerful than a flashgun such as the 580EXII, but I've seen thee quantums being used completely bare. I was wondering if they had some sort of diffuser built in? It seems like the front glass is frosted to provide a milky light, but I can't figure out why its still used bare bulb.

Any ideas?

 

[indolent]

theres lots of different mods for the quantum - if using with a brolly I use the reflector as a spill kill and bare bulb to get the max light. Lots of choice even a bare bulb enhancer to control light direction on a bare bulb.