I have played them, and cannot stand them.
The idea behind it has several reasons.
1 - All other instruments such as drums, brass, woodwind etc all get physically bigger as the pitch is lowered. Compare a trumpet to a tuba, or a snare to a kick drum.
Just like speakers, tweeters and subs. The sound emitting device is physically larger.
So therefore wouldn't it be logical to conclude that the strings should be longer as the pitch decreases?
2 - intonation.
Apparently it intonated better as the longer scale dilutes small inaccuracies in the larger strings.
3 - ergonomics. I had it sold to me by a luthier that builds these that to play an F bar chord on a normal guitar causes problems and pain and potential long term damage, whereas this allows your wrist to lazily flop into an F chord more naturally.
On all points I disagree.
First, the pitch / size argument.
If all strings were the same thickness, yes.
But what he overlooked was the fact that each string is already 'bigger' in it's diameter and physical mass. So the 'bigger for lower pitch' argument is redundant.
Second, the intonation.
The six string guitar I played had intonation problems on the G and low E strings.
Sound familiar?
If you know how to set up a normal guitar properly, it's not a big problem. And a simple thing like a compensated nut will do more for your intonation than fanned frets.
Third, feels like crap. It hurt.
I could not play many chords such as 9th chords (root, 5th, 9th) or bar chords comfortably.
Everyone is different, and it nay work for you, but after spending some time playing one I wouldnt take one if you gave it to me.
Hate em.
