I saw this at Road2CA. I personally didn't think it would be any more helpful than drawing with a pen or pencil. For the DSM (without a stitch regulator), much of the practice that you need has to do with getting a smooth motion, timing that motion with the speed of the needle to get even stitches. This method doesn't help with that aspect. It might help if you need to practice moving the fabric (paper) instead of the pencil. For the longarm, this tool requires that you hold the "handles" up over the table at just the right height to get the pen to the paper, without wobbling the tool, which I think would be very tiring, whereas with the longarm the handles are already at the right height and you are just moving them around. I could be wrong though and others might find the setup helpful. Here's the web address -
http://laliladesign.com/