I would say just as long as you find it helpful. Many donors don't use them. I did not even know about them but discovered on my own that wrapping a woolen scarf around myself help avoid incision pains. I donated 15 years ago by the long open cut (10 inches) so it really helped. It's not a safety of healing issue, but just a comfort issue. You might want to post also at the FaceBook page of Living Donors on Line, as more donors check in there.
Fr. Pat