Asides from the "novelty issue"....
Moderator Edit: As demonstrated in the posts following this one, most of the "information" presented in this post is false. In particular, it is absolutely illegal for a home user to replace the oil filter fitted to these types of silencers. /End Edit
On a serious note (ladies and gents) has anyone taken into account ... That not all "traps" are made equal??? By this i mean that there are design features on the inside of the filters (like metal bracing that is welded in place to route the oil into certain places and to hold the integrity of the walls in place)???? "Baffle-strikes" would be a joke in comparison when hitting these items in the hopes and attempt to get a hole in the middle of the filter so the subsequent ones would follow suit... Heat deformation of the dissimilar metals with inside the can..I can make a list, but I'm not going to. Please take a look at an used filter and ponder for a second what would happen if.... Lol!!!
Now, as far as the issue of the oil filter being the item in question.... I had contacted a BATFE rep at a local gunshow, and it was the most informative piece of information I had received from someone whose functions are to mainly guide and advice people to stay in the "good side of the law" because a visit from them would be costly no matter what.... But the "consumables" of the suppressor (wadding, screens, wipes to name a few ) are not considered part of the silencer since they are manufactured for a completely different purpose they do not fall under the scrutiny of the law (unless in this case, it is attached to an unregistered adapter). The adapter in itself is what would be considered a grey area object, since it has a "wink-wink" purpose and also could be used as a silencer part. The form 4 that would be filled out for this item (for it to be legal) and owned, the serial number on the adapter itself is what would be written down, not the filter attached to it because it would be considered a consumable that deteriorates after so many shots (wouldn't want to have a looooong paper trail tied to it every time you sent it back for another filter to be screwed onto it). So take it as you may.
As long as you don't change the shape, length (+\- .25") and the serialized info you are not required to mess with the ATF again for that suppressor.
Btw...there is a patent out for that, y'all should look it up ... Interesting read.