I know this sort of answer comes across as smart-alecky, but when I needed a harmonica for a film I just bought a harmonica. In fact I bought the Toots Mellow Tone Chromatic. It was hard to find in a web search but I finally found it at Sam Ash.
Harmonica's aren't that hard to play, espcially when you can do multiple takes and cut them together. I usually do my recordings one phrase at a time. Plus there are so many expressive things you can do with bending and breathing, that it would be really hard to do that with samples. I feel the same way about sampled guitars; there are some great libraries out there (Hello Chris Hein!) but its seems better and easier just to play a real guitar, even if you're not great at it.
the Zero G is mostly loops and phrases. The multisamples dont really sound that great.
the best harmonica i heard sofar is coming out of the Roland Fantom.
Its a 2 way velocity switch where high velocities trigger a sample that has a bit of pitchbending in the attack.
sounds quite convincing for a phrase or two.
It seems as though everything they had on that instrument has made it's way to their line of DVI's.
It has a good sound, but was watered down w/ DEF when they mapped it over to Muse.
I now believe Muse was designed to be a giant high quality GM. Many instruments are very nice, and others leave you wanting more.
It was first to the fight when GVI was released so I bought it. For 400 dollars it's great way to cover a gig for little money out of pocket. If a begginer was to buy this and use GVI's included content, it's a great way to get up and running quickly.
If they say it has more samples in the DVI form, I would say buy it. As the single DEF version on Muse sounds quite good, but lack articulations.