Well thats an interesting thread just read it all the way through, thanks for the information, good original post, I did not know about having to have a mark on the exhaust to prove it to be satisfactory.
For me personally small plates are a no no too, have never interested me and never will, I do however have a fairly loud exhaust and agree with the previous posts, that it does give u an extra bit of noticeability when people arent looking, a high vis jacket from hg and having lights on also works especially for long motorway journeys. I live in a very quiet ul de sac, and am also very aware not to come in revving the nuts out of the bike as it will just **** people off.
There has been times however when backfire from big exhausts both bikes and cars have nearly had me on the floor taking cover, so i can see why people do find them aggresive or scary. For me personally I will always ride quietly and efficiently in urban areas, well try to at least.
My personal view is that I think they do more good than harm, as long as they are not too defening, I think its very much up to the discression of the police or mot garage for recomendations.
I still think that anything that helps to get a biker noticed on the road more can only be a good thing.