Matth, Line width is not working ... (works only for Display Airport routes), but not for main airline display or additional airline display.
Also I do not understand the purpose of Show Circles ... those are just two static circles that do not change at all (at 800/1500 km) ...
Are they mean to show 800/1500 km ranges to hep with service profiles?
But then, you can change the distance under Range Circle, and any change you make is stacked one on top of another. Clicking Remove, removes all layers. Maybe a button "Remove" should remove them all, including the 800/1500 km range circle (imagine you want to just display a 2000 km rage circle... then the 800/1500 km range circles, which are static and displayed always, are causing confusion and clutter the view).
Btw it took me some playing with the tool to find out that the static circles are 800/1500 km circles.
P.S. Any way to use the "remove" button functionality (use din Remove Circles) in the option to "Display second airline"? That Remove button could (maybe) remove the stacked layers there as well, I would assume ... ? or not possible?