Dear Greg,
Thanks for the kind remarks!
Once the belly putter is planted somewhere in the gut, there are essentially two different ways to make the stroke. One is to use the arms to move the putter, with the shoulderframe staying pretty much the way it is at address. The other way is to move the shoulderframe the same way you would in a pendulum stroke, with the arms and hands in a "fixed triangle" that rocks with the shoulders.
There are two different pivots involved here. For the arms stroke, the pivot is the top of the putter handle in the gut. For the pendulum stroke, the pivot is the same as usual, in the base of the neck about which the shoulderframe pivots like a coathanger on a rod.
With the two pivots, there are two different "natural" tempoes. The arms pivot in the gut has a short pendulum length and a quickish tempo that encourages a fastish stroke pattern, with shorter stroke lengths back and thru. For the pendulum stroke with the pivot in the neck area, the stroke tempo and stroke lengths are the same as usual.
Also, with the pendulum style stroke with the belly putter, the hands CAN hang all the way down or can be higher up the handle with the elbows crooked. It doesn't matter too much since the arms and hands are dead and inactive. It's probably more comfortable to let the hands hang as far as they want to go before taking the grip in hand. The shoulders will be more relaxed that way, as holding the elbows crooked is a matter of constant tension in the pectoral muscles, the biceps, and the shoulder muscles. Either way, having the butt of the putter securely against the body helps keep the hands out of the stroke.
Using the arms-hand style stroke with the belly putter may keep the pivot more stable for some golfers, but using the hands encourages putterface twists and making the stroke run off line. Whether the ams style or the pendulum style has a MORE STABLE pivot is debatable.
On the one hand, with the arms style, it would seem easier to keep the hips and gut still since the upper torso is not moving. That would suggest the arms style has a more stable pivot. And with the pendulum style, the butt of the putter in the gut is not really the pivot -- the neck area is. Because of this, there is some question about what kind of stroke path you get when you rock the shoulderframe.
In the usual short-putter pendulum stroke, the butt of the putter points at the pivot or at least at some point in the sternum that is not too far below the neck, and the putter handle maintains this pointing direction at all times in the stroke. This allows a shoulderframe rocking that stays in a vertical plane, and the hands move a little farther away from the legs the farther the stroke goes so the hands can move straight back and thru.
With the belly putter in the gut, however, the distance from the body to the hands is fixed by the putter handle. This means that unless your gut is flat above the surface and the putter is aimed vertical at the ground (which it certainly won't be), the stroke path will curl back inside on the backstroke and curl back inside again in the thru-stroke, and you are actually prevented from moving the hands a little farther from the legs going back or thru, so the stroke cannot really be a straight path. So a belly putter would encourage an arcing or gating stroke path with either the arms style or the pendulum style stroke.
That being the case, the belly putter has less of a path that is straight, so the style depends more upon the stability of the pivot than the short-putter pendulum style does. That's a little counter-intuitive to the marketing spiel.
Another complication is that you still have to aim the putt, and make the stroke move the putter squarely thru the ball on the intended line, with good touch. Using the arms style belly putter, distance control becomes something of a problem on longer putts. And also on longer putts, the pendulum style stroke has its own problem, with the belly putter OR the conventional putter.
So, in the final analysis, the conventional putter and the belly putter are pretty close if using the pendulum stroke style. The conventional style makes it easier to keep the putter moving on line longer thru the hitting area, and the pivot control between the belly putter pendulum stroke and the conventional pendulum stroke is not all that different. The pivot is still in the neck. Advantage to the conventional method, due to less arcing in the path. Comparing the arms stroke with the belly putter to the conventional putter pendulum stroke, the added stability in the pivot of the belly putter is probably outweighed by activating the hands (always dangerous to the putterface and path).
The belly putter is really two different systems, depending on how you move the putter. All in all, it will help golfers who don't have good pivot control, but won't help golfers very much if they are already pretty good at managing the pivot.
Cheers!
Geoff Mangum
The PuttingZone
http://puttingzone.com
Golf's most advanced and comprehensive putting instruction.