Hi Mange, I just checked out the video demo on the Waves site for NX and it is interesting. You need a web cam first off for it to work as it works in line with your head position also the amount of light in a room will make an impact as in dimly lit rooms it won't work. As with other programs out there you can try different locations and speaker positions so nothing new there. I would say it would be good as a reference tool if you don't want to be trying the song out in other rooms or your car and such like but I would not mix with this tool myself. I personally like to know how the mix sounds to my ears as whether it is my own music or a clients music my judgement is why was chosen in front of others to do the mix. I think that anything that can get in the way of that process could cause problems later down the line.
My own strategy is that after mixing If I have used headphones then I will use my monitors first, then I will use a different pair of headphones I have with more Bass heavy EQ bias and then finally I have a small mono speaker and listen on there. If the mix sounds good to me on that speaker I know I have a good mix!