The Problem with Putter Inserts
Honu putters achieve superb feel by making the entire body and face from the same non-metallic material.
Some metal putters have face inserts made from some other material to improve feel. Many golfers notice distance control issues with inserts, often describing a strike as "clanky" or "dead", or just inconsistent. Some of this is due to the materials themselves, affected by temperature and even wear and warping of the insert material. Physically, many putters with inserts have a shallow face height that makes it easy to strike a ball on the rim above the insert, as illustrated below. Hitting the rim definitely results in a clanky feel and inconsistent distance.
I'll bet you know the putter I'm talking about. It's very common, from a big-name company. It comes in many different head shapes - "2-ball", rounded mallets, shallow rectangular heads, you name it. All of them have a similar face design with the same problem - the face is just not tall enough to reliably hit the insert. You can see this easily by putting a ball on a table next to the putter. The strike point at the ball equator is on the metal above the insert.
It's possible to design an insert putter with a higher face so you can't strike on the metal, but the world's most common insert putter gets it wrong! People find this hard to believe, assuming that major putter manufacturers must know what they are doing. But anybody can make a mistake and not realize it. Marketing makes more difference to a big company's bottom line than engineering. If something is selling, why mess with the recipe?
The obvious solution is to hold the putter a little above the ground so the insert strikes the ball, but many golfers have trouble doing that consistently.
Honu putters totally avoid this problem because the entire face is made from a material with wonderful feel. The face is tall enough to get a good strike point from a variety of "glide heights". I've tried other face materials but haven't found anything as good as bamboo.