Here is version 5 of UnwrapCylCurve, which works well, and required quite a bit more work.
Michaels angle script was used to calculate arclength, with better accuracy.
Processing each segment of a joined curve was done by using Michaels forum posted code.
Unwrapped segments have not been rejoined.
Unwrapped location depends upon curve start point. Incorporating bounding box center may improve this.
Comments are in the .js.
Test curves included joined helices of different pitch and handedness, as well as cylinder projected, circle and pentagon and small curve.

FLOW may be used to unwrap cylinder curves that are less than a single turn, using base profile circle and unwrap circle.
Such a Flow unwrap is slightly larger than an UnwrapCylCurve version, but the two unwrapped curves agree very well to a few decimal places and zoom_in's.

- Brian

The curve needs to be on the cylinder, a planar curve will probably yield no results...
A test ellipse in the top view, rotated in the front view, did yield a "boat hull cross section-like curve."
The script is a bit slow. It takes about 1 second per 100 numpoints, per segment.