Hey F4aceless, just this summer I did an exhaust change and I was in exactly the same position as you, stuck between the choice of Black Widow and Delkevic.
I started a thread
hereIn the end I went for the Delkevic, I bought the full system 450mm end pipe as linked
here. Others have said it might not be street legal but the website explicitly states that it is and they have been going a few years so they are probably legitimate (with baffle in of course).
I´m very happy with it, I also read around and heard people had had problems with alignment, indeed I set it up on the kitchen floor before heading out to the bike and the spacing did look a bit off, in the end it was perfect. Actually aligned better than the factory ones I took off. I had to persuade the old ones off but the Delkevic ones went right on. Instructions were a bit non-existant; there are 4 springs that need to be ?sprung? on that were a bit stiff, it comes with a handy tool which makes the job possible. The kit also includes new header gaskets.
One word of advice, get yourself some copper slip and some nice domed stainless nuts, putting the old rusty nuts back on the nice stainless header mounts doesn´t give a satisfactory finish. I did eventually get some but in the photos below I hadn´t got them yet:
ImgurLastly, with regards to getting the old nuts off, I watched a video by a guy I´ve been following on youtube which you might enjoy:
In the end I ordered a bottle of Automatic transmission fluid. Luckily I jhave access to Acetone at work. I made a 50/50 blend like the guy tested in the video and applied it with a pipette I also liberated from work, once a day for a week before. In the end the nuts came right off.
Best of luck