Eyedropper doesn't include the arrow heads on a line
If I have a line selected and I use the eyedropper on a different line with a stroke and arrow heads, it only copies the stroke not the arrow heads.
Please make it include the arrow heads.
Also, the most useful arrow head is number 27, it should be number 1 not number 27.
In fact, if there was a checkbox you could click in the stroke properties window that automatically changed a line to a measurement label so it put an arrowhead 27 on each end, changed the stroke to like 4pt yellow, and a text box half way along the line with the length of the line in millimetres, that would be so good! There is a tool in Sketchup with a measuring tape icon that does exactly this if you need a reference point.
The Eyedropper tool’s options can be configured to transfer arrowheads, which are treated as 'complex appearance'.
See comments for details.
Arrowheads are considered to be a part of 'complex appearance' of an object. Eyedropper in Illustrator by default is configured in a way it does not pick or apply the complex appearance, but you can change it.
Pick the tool, hit Enter to open its options (or double-click the tool icon in the tool panel), and tick both Appearance options. Now the tool is going to transfer all of the appearance from an object to another.
Be careful though — the behaviour of this 'advanced' eyedropper rather differs from its basic variant, especially when dealing with groups, so keep your eye on the Appearance panel. Don't forget to uncheck these option when you are done with the task.