Are putting rails, the ones that force the putterhead to go in a straight line, any good. Isn't it better to learn the stroke, instead of trying to force it. Or does it indelibly imprint the correct stroke into your muscle memory and make you a better putter.

The Eyeline product which consists of a mirror and guiding "fins" is absolutely brilliant. It forces correct muscle memory. I believe David Howell uses one regularly - say no more! Whenever my stroke starts going offline I have about 30 mins on it and the correct path gets grooved back in. I only do this about once a month, but I know more often would be beneficial.