I bought the Delta Putt for about $40. It arrived 2 days ago. To me this aid is so cool because it immediately show you if either your swing path or face angle is not dead solid perfect. It has three modes. am, pro, tour.
In a matter of an hour I figured out how to go from messing up sometimes on am mode to being able to consistently make good putts in tour mode.
For me, with the putter I was using, I needed more forward press, as otherwise I was rocking my shoulders fine, etc.
I also discovered with an other putter I have, the forward press was not necessary.
Yesterday I had my lowest score since March, 79.
While this aid does not so much address distance control or green reading, it gives you an easy way to ensure when you practice that. your path and face angle are perfect. A must have for us golf nuts. I am surprised this product has not received more attention.
PS if your path or face angle are not perfect to start, the beauty of this device is that it gives you the info you need to fix them (quickly).