I learned this from Ralph Eckert, and while this drill is seemingly simple it is so effective at building a nice smooth and confident stroke when practiced correctly. There are also many different ways to practice the drill and track your progress to keep things interesting.
Ralph suggests going this 3000 - 5000 times for best results - pretty hardcore, at 15 balls per drill that's 200 - 300 executions, even at 10 times a week that's 4 - 6 months! But trust me, if you take the time to do this twice a week, 3 - 5 executions per session, you will definitely see the benefits.
Great for all skill levels from beginner to expert, I put my time in with it and still do it occasionally. As I mention in the video, I find it sort of centering and use it if things get out of whack or when working on stroke or preshot routine changes. I've even done it with my eyes closed - that will REALLY build trust and let you know if your fundamentals are as good as you think they are...