First time twin shot for these two:
The one with all black hardware is a later 2013 made one, with a thinner soundboard, and a glossier black textured finish at the side and back. It produces a more open, more resonated and longer sustained sound. The sustain, especially for a strummed chord, is really long. No electronics.
The one with stock chrome tuner keys is an earlier 2012 made, a thicker soundboard, and duller finish for the side and back. The note doesn't ring as long, but is clear and good for the keb mo blues finglestyle play. And it is equipped with an AER AK15 Plus system by the dealer here as a demo piece.
Rationale for the difference in tone architecture? Well, my guess is the folks at Emerald might have listened to the feedback from owners and decided to improve on the design. Maybe Emerald wanna chip in some insight here?