All of these companies should have CRMI qualified instructors and UK CAA authorisation.
However the best CRMI course is given from actual airline experienced crewmembers who are the Instructors and who are experienced and knowledgeable.
Some companies have psychologists and researchers who know their stuff but do not necessarily have the actual practical experience to give realism to the modules and necessary skill acquisition. Being a CRM Instructor is about instructor skill acquisition and practical experience on the course not just knowledge acquisition.
Go for price, convenience and comfort with the experience of the instructors who run the course.
WAP