Strike Putts With a Square Face
If it's open at impact, the heel will make contact first. If it's closed, the toe will strike the penny-roll first. Either mishit will cause it to twist and bounce rather than roll. If the face meets the penny-roll flush, your face alignment at impact is perfect. And to make the cylinder roll straight down your intended line (it won't roll far, because it's heavy), you'll need to swing the putterhead so it approaches on a path directly along the target line and continues in this direction until after impact.
Finally, because the penny-roll weighs more than a golf ball, you'll be forced to keep your left wrist firm through impact and accelerate smoothly down the target line -- two excellent fundamentals exhibited by all good putters.