For what it's worth, I got a K4 the other month as my OEM box had sheared off the midpipe, and I needed a quick replacement. I also wanted a true dual, but didn't have (or feel the need) to spend £1100 or so on an Ark Grip.
The garage only took an hour to fit it and aside from it touching the ARB and needing a bit of heat/bending, the rest was fine. So yes it can potentially not be 100% perfect, but for the sake of saving a lot of money, it can offer an affordable true dual for the zed.
Time will tell how it holds up, but I don't drive in the wet anyway so it may last longer
And yes it is loud and can drone around the 1200rpm mark if you are in 6th and in traffic, but open it up and it sounds great