So, I'm gathering up materials for my headless build. I'm looking at truss rods, but i'm also considering either A. Some metal square tube like this STEWMAC.COM : Martin-style Non-adjustable Truss Rod
and B.(i'm leaning toward this over the tube)carbon fiber rods.
So my question is, why arnt not adjustable necks more common? Are there drawbacks that i'm not considering?
I live in a climate with the worst of the worst humidity, and yet well below freezing temps for 3 months of the year. The idea of a neck fixed perfectly flat and not moving are a pretty attractive option to me.
Also, the headless build i'm doing is intended to be ergonomic in everyway possible, including weight. So i'd prefer the carbon fiber rods, but i'm considering all my options.