I prefer a check chain in place of the top link. My land is undulating where I bush hog. A top link setup properly with rotary cutters swivel mount is not enough flex for me. I just have to be careful of PTO angles when it flexes alot. Ill hear it start to fuss, and Ill raise the 3 pt a hair to maintain PTO angle.
With bigger machines and bigger cutters a chain might not be a good idea. Wouldnt want 7-1000 pounds of rotating mass flipping over towards you if you got too bumpy.