As above. I have only done parts of it but never noticed anything too hard (I have only been riding 1 year and did it on a £200 Halfords full Sus at the time)
I have heard better things about Kiroughtree so if you are traveling to Scotland this is maybe one to concider. Black Craigs is about 14km long and full of some really tricky stuff from the videos I have seen.
If you are from “doon south” and making a journey all the way “oop north” I would read the Scotland Mountain biking guide that is in another Mountainj Bike mag this month (a much more infereire one I must add)( and it gives a good overview of all the trails.