Well, I'm not an expert, but I'll try to explain from what I know.
In hypnosis sessions you have a voice telling you to relax and visualize. Relaxation is very very important here, and so it is visualizing, not as if you were seeing a picture but "feeling it" the more realistically as you can. I mean feeling it as if you already had big breasts
Subliminals are recordings with suggestions masked by music. The suggestions are like "My breasts are getting larger" "my breasts are growing bigger" etc, but you can only hear the music. You don't have to relax while listening to them.
Supraliminals are the same as subliminals but recorded in a way that makes them more powerful -so says the site. Not sure if that's true or not, but there must be some difference because when I put them on repeat at night I always wake after 2 hours or so, but when I play normal subliminals I can sleep soundly.
Supraliminal Plus are a mix of subliminal and supraliminal but with audible suggestions, a different one in each ear. So they must be the most powerful.
I listen to this one in the morning, it makes me feel sexy
I bought the 10 CD set and some sub/supraliminals/plus in Spanish. And yeah it was expensive but my plan is to use them for many months, perhaps years, so it will eventually compensate!
I listen to the Supraliminal Plus in the morning, the hypnosis when I go to bed and I put a sub/supra on repeat during the night.
And I did like you, I first bought a single recording to see what it was like.
A few things I must say before I forget them LOL:
The hypnosis CDs are available only in English.
If you want mp3 and not cds you must send them and email saying so after your purchase.
Subliminals and supraliminals have an audible intro, so if you want something to put on repeat when people are around you you should get a silent sub/supraliminal (which I think are in English only) or purchase a French recording and ask them to remove the intro.
I always listen to them with headphones, but I think you can listen to subliminals without them.
You may want to read this:
http://www.deeptrancenow.com/hypnosis-cds-types.htm
http://www.deeptrancenow.com/enregistrement.html
I hope I helped you
PS: No, I don't get paid for writing this, lol, sometimes I sound like an advert (sorry)