I think if it worked as a silencer in any significant way, or significantly aided home manufacture of a working silencer, it would classify as a silencer and ATF would jump on it as an NFA-controlled item. From what I gather digging around (
http://thefiringline.com/forums/archive/index.php?t-398162.html), this already happened to one fake silencer manufacturer. So if you can legally buy it as a fake silencer, it must by definition be pretty much useless.
http://www.gpo.gov/fdsys/pkg/USCODE-2012-title18/pdf/USCODE-2012-title18-partI-chap44-sec921.pdf
(24) The terms ‘‘firearm silencer’’ and ‘‘firearm
muffler’’ mean any device for silencing, muffling,
or diminishing the report of a portable
firearm, including any combination of parts, designed
or redesigned, and intended for use in assembling
or fabricating a firearm silencer or
firearm muffler, and any part intended only for
use in such assembly or fabrication.