NO has a couple of positives.

- Doesn't force you into red
- Combos with more cards (~17 Green creatures + 4 Zeniths, rather than ~4 sources of Emrakul + 4 Zeniths)
- Elderscale is a safer plan than Emrakul against Dredge and Burn
- Potentially uncounterable with Boseiju + Cavern of Souls

Disadvantages:
- 2 for 1 yourself if you get countered or Progenitus is removed
- Slow clock, can't reasonably expect to race combo
- Vulnerable to more removal (Edicts, Council's Judgment, sweepers)
- Gives opponent chance to untap and either kill you or answer Progenitus, rather than killing them before they can react
- Worse hardcast late game plan due to colour requirements - not as easily enabled by Carpet of Flowers against Miracles
- Potential to leave you with dead cards in hand
- Need to resolve two spells (Creature, NO) rather than just one (Sneak).

IMO the benefits of Sneak are way more relevant, but if you want to play a combo deck in BUG colours I don't think there are many other options that fit in Nic Fit so I suppose NO is the way to go.