In the new issue of Golf Course Management there is a new study that takes a close look at the different Ball mark repair tools and what tool is the best for the job. I have taken many questions from members on which is the best and what tool I would like to see used. My answer has always been it is not the tool it is how you use it. This study basically shows the same thing. It is true that the "new" shorter tool when not used properly do less damage to the green, but all tools do an acceptable job repairing ball marks when they are used right. Please take a few minutes and read the article there is some great data.
All you have to do is click on the Ball mark heading and it will take you right there