I've been reading about 3 point hydraulic top links. Some of them come with check valves to keep them from moving.
I also read that some loaders if not all have check systems for safety. quote]
Would you be able to say which tractors have the check systems that you are talking about?

(DPOCV I am assuming) I am fairly sure that none of the scut, cut or utility tractors that are talked about on this forum have any safety check valves on their FEL. I'm not sure if even the industrial TLB have them, I know that my Mahindras and our Case 580E doesn't.