The principal is slightly effective in making some of the stuff clump together, but people have shown me the state of the pipe where its been fitted almost completely blocked by gunk. I mean there is no way such a simple device can remove anything and therefore it has to end up somewhere, so its probably effective for a while till the grot builds up then flakes of it start to detach and gum up the works further on. Its a typical snake oil idea, ie a quick demonstratable fix that will be of limited use long term but by then the money has been pent.
The bottom line is you need to ask anything that looks too good to be true, fine but where does the stuff it takes out actually go then? That is when they start to babble rubbish. Brian