I have done my apprenticeship 2330 NVQ etc and I used them just to get the 17th. The course they gave me wasn't great a lot of mistakes. However I had learnt the regs and have good working knowledge so I went with it.
My college wouldn't let us just sit the exam as any failures looked bad apparently.
So my choice was 400 quid and off work for 3 days which would of used up holiday time haha (I have a little boy so I like to use it wisely). Or spend 130 quid and pop and get it done on a Saturday morning.
Job done passed with flying colours and now have the 17th to go with my apprenticeship.
This helped me secure my new job as a sparks in a factory. Now taking on a new side of the industry as a trainee electrical/mechanical engineer. Back to day release.
To sum up. Use these if you know the regs and can't find anywhere to just sit the exam. If you don't know the regs go back to college and take the proper course.