Homer Kelley recommended that all instructors build an Inclined Plane for use with students. He himself said that until he built one of his own, he could not truly visualize the [three-dimensional] path that the club needed to take.
I like using the dual track adjustable swing plane trainer with many of my students to visualize the [three-dimensional] path of the club head. I use the dual track a little different as I do not have the shaft on the rail. I will set the dual track up in a very vertical position and have the golfer set up so that there is 6 to 8 inches of space between the club shaft and the rail. I will then have the golfer make back swings and have them maintain the space between the rail and the club shaft.
Most golfers will take the club head inside during the start up and hit the dual track rail the first few back swings but it does not take long for the golfer to understand how much up there needs to be so they won’t hit the rail on the dual track. I have found this is a great way for the golfer to not only see the 3-D start up move but to do it. After a few minutes I will have the golfer set up with the shaft closer to the rail of the dual track about 3-4 inches and make back swings.
I will then do the same process for the down swing. When it looks like the golfer is getting it I will have them set up with the shaft now about 18 inches off the rail and hit balls. Training the golfer this way with the dual track produces some of the fastest results I have ever seen in 10 to 20 minutes. You might want to get a dual track and try this. It will cost less than building a plane board and it is light and adjustable as well.