What I really like about iAwake is their standalone offerings. They produce quite a few audio pieces that are geared toward specific brainwave targets and desired results. These individual products aren't progression - based (you can listen to whatever tracks you want whenever you want), so there's no lengthy investment of your time involved. Also they're way cheaper (around $30-$50 depending on the product). In addition to manipulating brainwaves with sound, they pride themselves on their patented Biofield tech (look them up for more info).
When making an educated decision on what product is best for you, it is important to have a general understanding of how the technology works, and what the benefits are of visiting the specific brainwave states.  Please click the link to visit a more detailed article –  How Does Brainwave Entrainment  Work, and the benefits of Alpha, Theta, Delta, and Gamma brainwaves.
In 1984 medical researcher Dr. Gene W. Brockopp published a paper making several conclusions of audio and visual entrainment (AVE). Such conclusions were that hemispheric synchronization caused by AVE is related to increased intellectual functioning, practiced use of AVE overtime leads to a cumulative effect, and AVE may result in the recovery of early childhood experiences.
The activity of neurons generate electric currents; and the synchronous action of neural ensembles in the cerebral cortex, comprising large numbers of neurons, produce macroscopic oscillations. These phenomena can be monitored and graphically documented by an electroencephalogram (EEG). The electroencephalographic representations of those oscillations are typically denoted by the term 'brainwaves' in common parlance.[4][5]