The great thing about nada/sound of silence is that it becomes louder the more concentration you have and provides useful feedback loop for your meditation. It is reassuring to hear the celestial sounding noise get louder as you meditate.
However, I did not find it skillful for maintaining mindfulness during the day. I had difficulty hearing the nada sound if there was noise around, like in the shower or in traffic.
Supposedly, it is possible develop this to the point where you can hear the nada sound in noisy situations.
The below book has a couple of good chapters on it including how to maintain your attention to the nada sound throughout the day.
The Law of Attention: Nada Yoga and the Way of Inner Vigilancehttp://www.amazon.com/The-Law-Attention ... 1594773041