All a company has to do to get a course accredited is to pay £x to an insurance company who will agree to provide cover to students attending the course. It’s a great money making opportunity and totally legal.
There are no minimum standards of teaching required, no requirement to meet industry guidelines or any serious quality assurance involved and no guarantee that you will be competent afterwards. You’re also effectively tied to one insurer forever as other insurance companies might not be willing to cover you without a nationally recognised qualification such as an NVQ.
On the other hand, some courses that are set up this way are excellent and their teaching is of a very high standard but you will only discover this from extensive research using other external sources and not via the glowing reviews on the company’s own website. Companies such as CND, Young Nails, Nail Harmony etc. do have a well earned reputation to maintain so that is also worth considering.
Really, you need to ask yourself why does it take a minimum of a years training to gain an NVQ yet here you’re going to be fully trained and ready to work on paying clients in 5 days? If the training is really excellent and you have a natural talent, then it’s possible, but do plenty of research before you sign up.