The O-Port sound hole plug

[ejbpesca]

Anyone use one of these fluted anti feedback sound hole plugs? It is also supposed to boost sound not plugged in. Did you find it worth anything for your acoustic guitar? I understand they do not fit all guitars but I wonder if they just are a gimmick or truly a sound enhancing/feedback fighting device. Opinions on the O-Port appreciated. I think they are made by Planet Waves.