I have been using Dr Andrew McLean's techniques for 15 years. They are excellent. His is the only current system which is based on scientific research in horse and animal behavior, though more trainers are starting to use these ideas. The principles on which the system is based are universal and apply to all training methods and all horses. They can be applied to natural horsemanship and conventional training systems.
They are based on the lastest research into how horses learn, how they perceive the world (sight, sound, touch, move etc) and biomechanics.
The system is genuinely based on putting horse welfare as the top priority. It puts how the horse responds at the centre of all cues and techniques, and if the horse doesn't do what is asked, it is always up to the trainer to work out why, rather than blame the horse for being disrespectful or arrogant.
The universal training principles which were developed by Dr McLean and Professor Paul McGreevy have since been adopted by the International Society for Equitation Science which is a group of world leading equine behavior scientists, many of whom are also professional horse trainers as well.
The training principles can be found here: Learning theory in equitation
For me personally, using this approach has taken me from a nervous one horse rider to a business staring client horses and taking in difficult horses for retraining. I haven't had to spend a fortune on equipment or expensive books and DVDs and I can reliably get the same results time after time. The specific techiques that Dr McLean uses are focussed on dressage because that's his background but they are very simple and easy to apply. The principles on which the techniques are based however are universal and can be adpated to any discipline or system.