Light Diffuser, pro's & con's

I have spent the last four hours trying to find out the actual tested results of light diffusers, and can't find any real data from growers. I would appreciate it if anyone has any thoughts on these that have used them. Do they actually give you better distribution with less hot spots? I am talking about the metal "shield" that goes around the base of the socket and sits just below the bulb, with lots of holes in it. I would greatly appreciate any and all input on this subject. Thanks in advance for your time.