I tried 20 shots - minimum buy.
My impression is that it may be a most valuable aid when calibrating clubs - you will never get a more precise 50/60/70% shot than with this pal.
In regular play, IMHO, too many shots are wasted being 100%, all drives and at least the second shots on Par 5s, and 95% approach should be possible without it. Thus there are only a few special shots left, in short game, and this doesn't look effective to me.
It's also a rise of 5 crs per nine hole round of 50 shots. Not much, but it adds over time.