I've got the scorpion on mine, came fitted from the previous owner. My first impression was I thought it was a little quiet compared to the Miltek I had fitted to my previous Zed.
Since then I've fitted decats and a Y-pipe from Tarmac sportz. It now, in my opinion sounds a lot better. Still not over the top driving 'normally'. But loud enough when you want it to be.
I live in Harwich, If your local I'd be more than happy to take you out so you can have a listen for yourself.
If you do decide to go for the scorpion, I may be able to get you one for a good price as a friend bought one but then sold his zed a week later so didn't even fit it!