One key to good golf is a consistent setup. I have found the Eyeline Slide Guide essential for creating a repeatable setup for ball and foot placement during practice sessions on the putting green. The tool adjusts easily, comes apart into two pieces, and stores in the included nylon sleeve. The Slide Guide is extremely light-weight and easily fits in a golf bag or practice duffle. The Slide Guide markings assist with adjusting the tool to your specifications each session. Alternately, you can mark your own settings with a marking pen at the connecting slide on the reverse, white, unmarked side of the Slide Guide. I have found the Slide Guide an indispensable part of my traing aide tool box.
I think this is an effective tool; I tend to align to the right and the tool assists in making corrections.