I spent a few minutes in Capture NX2 trying to get the ADL effect in post. I used an image with ADL High to maximize the effect and make it easier to see.
The first step was to turn off ADL. This left me with an image 2/3 stops underexposed. Using a variety of editing steps, I tried to lighten shadows and protect highlights to create a similar result, but it was quite difficult and required a lot of trial and error. In the end I liked the ADL version better and it represented a better starting point for other editing.
What appears to be happening in the ADL algorithm is that blacks are maintained, whites are reduced from a value of 251 in my exposure to approximately 236 for ADL High (increments of roughly 5 per step for Low, Normal and High). So the lower exposure is offset by the algorithm to extend the effective dynamic range. I'll need to try additional testing with an image that has blown highlights under normal circumstances to see if ADL truly extends the DR.
Based on this test, I'm rethinking my choice to not use ADL. I think that like Mick, using ADL on Low is a better answer.
ADL Low did not adjust the exposure in my testing. That removes the "black box" issue on exposure. It also means that if I turn off ADL in post, I am left with my original exposure.
Using ADL on Low preserves the right to adjust it with other settings.
I would also use ADL if I was shooting JPEG's. My default setting would probably be ADL Low but I would willingly use alternate settings as needed.
If I was using an editor other than Capture, I would leave ADL turned off since the editor did not honor the ADL settings and there woudl be no advantage. Using other editors, ADL Normal or High would just leave me with underexposed images.
It's possible that ADL creates a little noise in shadows, but the noise appears to be something that can easily be dealt with in editing.