I tried it !!

Yes! At last, I have tried using MetroNap (the machine I mentioned before). The semi-circle plate outside could be turned around to cover my face. I could control the position of the bed, and volume of songs.

Although it's look very fascinating, it's not that good. From the advertisement, I shouldn't hear anything from outside, but the result is I still heard sound from outside. By the way, the dim light and slow classic songs could help a lot in making one sleep. My rating is only 3 stars from 5. :D