I was wondering the same thing. Couldn't find any samples or feedback or anything. I do think that ultimately how convincing you sound will rest on how accurate your inflection and accent are. A voice mod may just help overcome any problems stemming from muffled speech.
So I've been looking at masks for a couple of weeks now and have mostly settled on the GCFX one (listed here
http://www.ebay.com/itm/Bane-Mask-F...1026831133?pt=US_Costumes&hash=item3f1a753f1d), however, like a lot of the other masks it seems to run fairly large. I've got a small head for a guy my size (22 or so), how much of a problem would that be? I realize the material is supposed to be fairly tight and stretch to the person wearing it, but I'm worried that 3 sizes difference may be too much to comfortably overcome with padding. I definitely don't want to dump 300 dollars on a mask only to have it look horrible (obviously).
I'd wait for these new masks to come out but I actually need mine by August 15th or so for a convention. Kind of deciding what to do... any thoughts?