Double Neck Console Guitars – What’s important to you?

What is important to you when considering a double neck guitar?  What vintage models have inspired you and why?  What tuning on each neck do you use that require the use of a double neck?

I was especially inspired by the beauty of the old double neck National Guitar.  The difficulty for me was the narrow string spacing but when designing the Caladesi Double neck that was easy to remedy.

I use a C6th tuning for the neck closes to me because that is my primary tuning.  But I have a growing interest in B11 because it allows you to play some beautiful enriched chords that can stand alone or augment what I am playing on the C6th neck.