I don't own this device nor have I heard it. I do remember reading a review of it a while back - mildly interesting.
My thought is that it's not that hard to make a surface (diaphragm) vibrate at 7.83 Hz and this will "attempt" to create a 7.83 Hz waveform. Just because the wave cannot fully propagate in a given space doesn't meant that it's not having an audible effect in that space. If the company claims that there is a complete 7.83 Hz wave in that room then they need to go back to physics class. Also remember though that the lower the the frequency, the more acoustically transparent walls would be to that wave.
Note that this doesn't address the amplitude of the wave produced. The size of the "driver/diaphragm" would directly impact that (as was indirectly pointed out by Bluewolf in the OP). So, even though the wave will propagate outside of the room, I doubt the amplitude of the wave would be very large.
My thought is that it's not that hard to make a surface (diaphragm) vibrate at 7.83 Hz and this will "attempt" to create a 7.83 Hz waveform. Just because the wave cannot fully propagate in a given space doesn't meant that it's not having an audible effect in that space. If the company claims that there is a complete 7.83 Hz wave in that room then they need to go back to physics class. Also remember though that the lower the the frequency, the more acoustically transparent walls would be to that wave.
Note that this doesn't address the amplitude of the wave produced. The size of the "driver/diaphragm" would directly impact that (as was indirectly pointed out by Bluewolf in the OP). So, even though the wave will propagate outside of the room, I doubt the amplitude of the wave would be very large.