Personally, I think it's a great idea, and very practical. My band plays several songs that were originally in alternate tunings, and I either have to fake it in standard tuning, or bring multiple guitars (I usually end up faking it, real estate on stage is a premium in a 5 piece w/ steel guitar). Ideally, I'd have one guitar in standard A440, one a half step down, one in open G, and one in open E; however, that will likely never happen. I have my main guitar in A440 with a backup in its case and one in open E. Songs in open G (lots of Stones songs) I just fake in A440, and songs that we should really do a half step down (to facilitate vocal range), we just do in A440, which kills your vocal chords towards the end of the last set.
If it really works like it does in the demo video, I'd love one! It would make it so much easier to cover lots of songs the right way, and any extra space to move on stage is a good thing in my book.
-David