I think that guitar makers have learned a great deal about how to improve the quality of a guitars sound, by using different construction techniques, design, and materials. Gut strings do not sound very full as compared to nylon, nor do they last or stay in tune very well.
The instrument shown is an interesting curiosity, and has value as a historical item. The guitarist plays well, but I had a teacher named Andres Segovia, who would not have allowed anyone in his presence to use the right thumb as this guitarist does. The right thumb should be placed in front of the other fingers of the right hand, like a hitch hikers sign.
The acoustics of the room did not allow for a true appreciation of the instrument.
Tom