I thought of using my cnc conversion in manual mode - forget it, once you go cnc you don't go back - it's easier for me now to type a couple of lines of g-code than it is to twiddle the hand-cranks
My screws were knackered so my decision was easier, if your screws and nuts are new then they might work ok in a cnc but you will have more backlash as they need it for clearance, ballscrews have none.