Thomas, as always Mr H did a grand job so if you do go down this route, he's your man. Just don't try and be helpful and take along your own Dremel - he takes the pi$$ out of its puniness beside his ~25 BHP die grinder 😬.
As for the quality, I don't know what John thought, but it looked good to me: all the holes were in the right place and everything fitted (all we (well, John) had to do was drill another hole in the front mounting bracket). The finish looks impeccable.
As for noise, I wouldn't have said there was much in it either way. The Powerspeed makes a slightly deeper, less tinny, noise. If anything, it's slightly quieter I'd say (all very subjective though). As for performance, it's made a noticeable difference. As somebody else posted a while back, the engine is more 'free' and much less asthmatic (remember though that I switched from the 4-1-inside-the-body exhaust). Previously, I got a shove in the back at about 4700 rpm and that's now less pronounced as there's more oomph lower down.
FWIW,
Adam