do f-mods work?

jl harrison labratories makes a crossover known as an f-mod it goes in line with your RCA and filters out either high or low frequency.These are available on parts express web site.I want to know if any one knows anything about them.Are they worth it do they work? Any knowledge is appreciated.
Yes I have tried the PF-mods/2W1 and while they do work, they are not very high quality and one can only use cheap IC's with molded RCA plugs as the plug spacing/opening is too tight/small. I had to remove the shell to use them with my AQ and Audio Magic IC's. Also, the soundstage shrunk considerably and they added a haze/grain overlay to the music. Of course, YMMV...
Thanks Nmmusicman I DEFINATELY dont want ANY of that!