I was comparing Neo and Mojo vibe some time ago. Neo was better sounding with clean guitar or just to a cranked amp.
It does the heart beat phasing really well. Mojo is milder, not that prominent phasingwise.
when i placed a fuzz unit before them, then Mojo processed the fuzzed signal much better - it was smooth and nice.
Neo doesn't work well with the fuzz unit placedin front of it. The sound is somehow swashy, swirling .... say ugly.
What can make the difference? The LDRs? The signal path of both these Vibes is almost the same, with a few minor value differences.