We have one in our studio (and also sell these - have sold a bunch to a lot of people including Leo Sayer and Augie March)..
we purchased one and used one before we decided to start selling them - just letting you know all of this to try and be as unbiased as possible!!
we love ours - it basically takes out the bad reflections and filters through the good ones (if that makes sense?!).. you don't notice so much on a single vocal but once you start layering vocals you can really hear the difference in the "mud" that usually builds up with the reflections. it does not "colour" the sound as HA_DA_JA said he heard, to me it basically controls the sound to be more pleasing especially on multiple vocals.
I have used it on guitar cabinets, in front of kick drums and also on vocals. We lent one to Garth Porter who also had great success using it with 2 x brass players side by side to help seperate their instruments.
here is our listing:
http://cgi.ebay.com.au/sE-Reflexion-Fil ... dZViewItem
also another product that does more isolation rather than filter:
http://cgi.ebay.com.au/The-MIC-Thing-Fl ... dZViewItem
hope this helps, and hope this doesn't overstep the boundaries of this forum.
Cheers
Geoff Mison
PONY MUSIC