Beyond all the 'states of consciousness' debates and how stupid it is that anyone is worried about this (people have used it to meditate for years) this is very scientific.
What they are really doing is just building a poor mans sensory deprivation tank.
Your mind generally keeps track of where your body is by a few things, effects of gravity, vision, and most importantly your body's 'gyroscope' is the inner ear.
By laying down on something soft and not moving you partially remove gravity (true sensory deprivation tanks suspend you in a liquid to do this and thus are far more effective).
By covering your eyes completely you remove vision as a positional reference.
Bi-aural sound effects can induce certain types of brain waves, but they also throw your inner ear gyroscope all out of wack.
Combine the 3 and you've removed your brain's ability to understand where your body is and in what position its in.
This is where the 'out of body' feeling comes from, without a grounding reference the rest of your brain is free to introduce sensations of movement. If you imagine your flying like a bird your brain no longer has a grounding point saying 'you know man, your not REALLY flying'.
The rest of the audio in these tracks in there to 'guide' you into a mental state, induce certain types of brain wave usually with the goal of inducing a lucid dreaming type of state.
Some people tweak out because of this, generally people that hate feeling out of control. Sensory Deprivation tanks have even been used a form of torture. You can also purchase time in them commercially to relax, some spa's have them.
Some people love it, and the people that love it probably are more likely the ones who are also into other forms of mind altering (drugs or whatever). Not that i'm saying its a 'gateway' to anything, if your the type of person that loves this type of experience you don't need a gateway, your already wired to enjoy these things, which is good in my opinion. Everyone needs to let go sometimes.