I'd have a go with the granulated absorbent. My concern was the steady wicking action, I'm not positive it's a good thing for eggs. In a perverse twist, the eggs like humidity but not necessarily a direct draw. I would worry that as the egg absorbed it would form a positive pressure flow (like roots do in the soil) and then be continuously absorbing. Then again, I've only used blocks of rockwool a handful of times for propagating veggies.

I thought about trying this, but in the end went with what I knew would work. If you are serious about doing it and this is your first season with eggs, maybe split the clutch and do half the eggs in rockwool and half a traditional way. That way if it backfires, you don't lose the whole clutch. Keep us posted if you have a go.

Cheers,
Kat