Honu putters are finely balanced so the club doesn't try to twist in your hands. That makes it easy to keep the face aligned with the target. When you putt with a Honu, the club obeys your every command, without the "will of its own" that is common to most other putters.
If you're keen on the gory details, read on. It gets technical below.
The Honu is balanced by putting its shaft directly through the putter head's center of mass. The center of mass is the spot where there is an equal amount of mass (weight) on either side of that spot, in any direction. Every Honu is custom-drilled for this according to the customer's fitting specs.
If a putter shaft is off-center (mass-wise), two forces fight you for control of the putter. The first is gravity. Gravity pulls on the center of mass, trying to make it go as low as possible. If the shaft goes right through that center of mass, gravity pulls directly along the shaft so there is no twisting force. Conversely, if the shaft is away from the center of mass, there's a twisting force as gravity tries to move the center of mass to a different place. You have to compensate for that twisting with your hands.
The second force is dynamic torque. Even ignoring gravity, as you move the shaft, the center of mass tries to "lag behind" the shaft. To understand this, think of pulling a rock with a string. The rock will "get behind" the string no matter which direction you go. In a putting stroke, the putter will try to rotate in one direction as you go back, and in the other direction as you go forward. The putter wobbles as you move it. You have to compensate for this wobble with your hands, separately from the gravity compensation. It changes for different tempos. That's why you tend to "push it" when you "ease up" on a slippery down-hiller, and "pull it" when you try to "ram it in the hole".
Dynamic torque balance is subtly different from static center of mass balance, corresponding to the way that car tires must be "spin balanced" to prevent shaking at high speeds. Honu putters achieve both kinds of balance.
Honu putters require no compensations. They don't twist under gravity, and they don't wobble when you move them back and forth. You can hold a Honu as lightly as you want and it will still putt true. Tension-free putting!
Center mass balancing is an old and proven idea for any number of things including putters but no one prior to Honu has mastered the build technique, the science, the fitting method for putters and with precision to still remain mass balanced. The Honu putter is catching on because of its amazingly good feel, its superior science, its superb balance, and its ability to be fit to any player, and likewise offer superior and provable performance benefits. Honu goes beyond just high MOI (resistance to twisting on off center strikes) it has no twisting force at impact or twisting force of the entire club due to gravity or torque whatsoever.
Common (Un)Balancing Schemes
Perhap you've heard of "face balanced", "toe down" and, lately, "toe up" putters. They are different balancing approaches. The names refer to what happens when you rest a putter shaft horizontally across your fingers, letting it rotate freely. A face-balanced putter will come to rest with the face pointing at the sky. A toe-down putter will stop with the toe pointing more or less toward the ground, while a toe-up putter is just the opposite, with the toe pointing to the sky.
What causes it? Weight (mass) tries to "fall to the ground", i.e. to get as low as it can. There are two places on the putter that matter.
The first place is the "center of mass". For a complicated shape, you can pretend that all the mass is concentrated at a single point, where there is the same amount of weight on any side. That's the place that tries to "get as low as possible".
The second place is the "hang point". If you sight down the shaft, ignoring any connection gadgets or bends near the head, and find where that sight line intersects the putter head, that's the "hang point" that supports the putter.
When you rest the shaft on your fingers and let it rotate freely, the center of mass will end up directly below the hang point. The videos below are computer simulations showing how this works for toe-down and face-balanced putters..
There's no simulation for the toe-up case because it would be boring. In a toe-up putter, the center of mass is already below the hang point, so when you start with the toe pointing up, it just stays there.
That might seem like a good thing, and to some extent it is, since it uses gravity to keep the face aligned in a plausible position. But there's a catch.
Since the center of mass is away from the shaft, toe-down putters still suffer from the "dynamic torque" wobble described above. The putter tries to twist as you move it.
The only way to avoid both gravity twist and dynamic torque wobble is with center-of-mass balancing.