EEG training is more complex to learn and do. There are some basic skills to learn, but with support a lay trainer can gather the data for their QEEG and train a whole-brain plan. For physical issues like sleep or pain, for emotional issues, trauma, meditative states, etc. EEG is an important part of training. Both together are ideal.
Most professionals will use the whole package. Many home trainers—especially those working on primarily cognitive issues of mental performance in younger brains, may find HEG is all they need. It is possible to buy an HEG system initially, choosing an amplifier with the ability to do EEG also, and then add EEG if and when desired without a major additional cost.