I had the fake rails and as mentioned they are glued on. They also clip on quite snuggly to the roof studs which are M6 so require a firm pull to remove. The glue is a pain to remove, I soaked mine in citrus solvent for a while which softens it making it easier to remove with a plastic scraper. Also with the studs remember the remove all the paint on the threads, a die works well if you have one.
As to using the factory roof racks, they are known to create cracks in the roof around the studs which can cause roof leaks and by having a good look at them I would agree, they are not the solidest of things. That's why I built my own Prinsu style rack out of stainless and alloy which is so ridiculously solid with zero flex or movement which is the issue with the factory racks, they flex too much when loaded up. I have a roof top tent on mine and 270 awning so it needed it to be really solid.
Oh and remember to put some silicone under the rails when fitting whichever route you go and be mindful our KK's only have a 72kg roof load limit. Good luck.
