I have had both japspeed and scorpion and I will say scorpion is a much better system although they don't do a y-pipe. The scorpion will come with a lifetime warranty if bought new and usually around 330quid new.
The fitment issue is to do with the pipe alignment and as with most aftermarket exhausts some look better than others fitment wise. You may find a k2 which fits perfect and vice versa, it really is just luck.
I much prefer the scorpion, looks like stock, still looks new after a year of having the balls ripped out it and it's getting better sounding with every extra mile that's put on it.
Value for money I'd say scorpion mainly due to the lifetime warranty and ease of fitting