According to reviews I read ... Putting the deafness issue aside, it either works .. Some babies like it and end up being angels- easy to handle after birth, alert and calm etc. or it doesn't - in which case the babies are monsters - hard to manage, cry a lot and throw lots of tantrums after they are born.
Think of it this way. It's a constant repetitive beat , there are variations but it's still a constant repetitive beat, you use it twice a day for 1/2 hour each session, for months...Will you personally enjoy that ?
The issue is (in my opinion) , the baby is passive, it can't get away from the source of the noise even it hates it, and there's no way for him to tell you! Can you imagine someone subjecting you to noise you dislike forceably for an hour each day? the beats are static and non interactive, ie you don't interact with the baby, which definitely doesn't help with bonding...
And in terms of interacting with the outside environment you are better off doing proven activities like singing, playing music to the baby and reading to it in utero..
There's actually another method of prenatal education that I am now researching. it involves the use of a small drum and xylophone ... And it's completely interactive to use meaning you are communicating with the baby when you use it and it's not a one way street.. That's a much better model in my opinion !