On the eighth hole I asked my two partners to try the marked ball. I can't believe I can acturally putt again. My concentration increases as I place my ball on the green with the line pointing in the selected direction, and my concentration continues as I evaluate how true I hit the ball by observing whether or not the line wobbles. Not just in the right direction, but rolling period. It helps with mechanics.
People come in the shop, look at it, and laugh.
Then they try it and are amazed. Note that some prominent PGA and LPGA Tour Players are seen putting with a line on their ball to align their putts.