The ERG Theory recognizes that people are different and there are variables that can affect the needs of an individual. In other cultures for instance, they rank needs differently than in the US. In the US alone depending on your upbringing and background an individual may hold certain needs of more importance than others. It also allows there to be an increase in flexibility and it is less restrictive than the need hierarchy by Maslow.
The ERG theory is a relatively new concept compared to Maslow’s theory and aside from Alderfer’s research there hasn’t been much research on the theory. As in any science, critics want to see the facts based on research. With only one man's research then tend to be skeptical of the actual worth of the theory. The ERG theory allows individuals to simultaneously satisfy any of the needs, to know this you would have to assess the individual to see what motivated the person to behave a certain way and then determine what need was most important to the person. This information may be very difficult to obtain because much time would need to be spent with the subject.