The ifrothgolf review
A flat aim-line board you set down a foot or so behind the ball. You place two of the supplied steel marbles to form a narrow gate just ahead of the ball, line up the printed aim line to your target, and putt. If your start line and face angle are square, the ball rolls cleanly through the gate. Push or pull it even slightly and the ball clips a marble, which rattles away and tells you instantly that you missed. The board also has dots for checking your eye position over the ball, and it doubles as a green-reading reference because every putt has to start on a straight line first.
What's great
The feedback is honest and immediate in a way a mirror never is. A mirror tells you your setup looks right; the marble gate tells you whether the ball actually left the face on line, which is the bit that decides whether putts drop. It is dead simple, packs flat into a carry case, and works on an indoor mat or the practice green. Narrowing the gate as you improve gives you a built-in difficulty dial, so it stays useful long after the early wins.
Worth knowing
It only trains the first few inches of the stroke, so it is a start-line and contact tool, not a distance or long-lag trainer. The loose marbles are easy to lose and a pain to chase on a real green, especially in any breeze or on slower carpet. It rewards a straight putt, so if your intended putt has real break you have to aim the board at your start line rather than the hole, which trips some people up at first. And the board needs a genuinely flat, true surface to give clean readings.
The verdict
One of the most honest putting aids going for short-range start line and strike, because the marbles cannot lie. If your misses come from starting putts off line it is well worth the modest outlay, just know it does nothing for distance control and keep a few spare marbles handy.
