What is it? Whats the difference? Any good?

 

I am not sure if this is what you are talking about but...

Most dirt bikes have a plastic throttle tube for the twist throttle. After a hard right-handed crash, they are prone to breaking, warping, cracking, and deflection which causes drag when you twist it. You can replace the flimsy plastic throttle tube with a billet aluminum tube for better wear resistance and crash protection.

It is not necessarily the billet being good as much as it just being metal that makes it better than stock plastic. Most cross country riders use bark busters already. I see the billet tube being good for crash prone moto-crossers...

 

I don't know..I see the thumb throttle being changed in "Dirt Wheels" all the time for billet thumb throttles. I don't know what the advantages were.