Since 1ml is approximately 10 sprays, then 100ml would be 1000 sprays, right? That's a lot of fingerwork!

Me, I'd just get too impatient and would probably end up putting a hole in the bottle and pouring it out.
I've never decanted myself, but someone once told me you should measure your decant atomizers to make sure how much you should fill it up to reach exactly 10ml or whatever, otherwise you might be left with nothing after the second last decant.