[squirrel_hunter]

So to answer your questions, firstly I doubt very much that you will notice any difference in fuel efficiency (and from a personal viewpoint I consider that lower fuel efficiency is directly proportional to the amount of fun you are having).
Yes it will sound like a sewing machine with the stock can on.
The weight won't be noticeable and even if you did you'd get used to it pretty quickly.
Reinstalling the original is straight forward, you just need an adaptor providing the cut was well placed originally, or if its a full replacement of the original just hope you can remove the exhaust studs.
Road legal is a grey area.
Don't sound like a yobbo it gives us all a bad name.

My advise, fit a universal baffle if you can't locate the cans manufacturer and order one from them.