If you're after honest advice here it is.
I spent a considerable amount of money 'retraining' as a plumber. Had I done a bit more research before, all of the information on the course was freely available on the internet.
I did a course with OLCI. They passed everyone and anyone who came through the door, so in effect the end qualification was worthless.
I would have liked to secure work with a plumbing company afterwards, but nobody would take me on as I was 'just another person doing a fast-track course'. Please realise, you come away from this course with nothing apart from some limited knowledge. What you learn on this course is such a far cry from plumbing in real houses.
This said, you certainly can be a success doing these courses and working on your own. It takes a LOT of hard work and I don't mind saying some stressful experiences. My first year was very stressful but now I am a confident plumber and I do all my own
tiling/carpentry etc as well. Over the last 6 months I have stopped advertising and all my work is from my website or word of mouth.
As long as you recognise that the course you will be doing isn't worth the paper it's written on and that your first year will be very, very hard then it's worth considering.
I don't believe you need to do a 4-year apprenticeship to become a good plumber but the point is valid that you do need experience. 1 year should do the job in my opinion. That said, you never stop learning - the learnings just become less frequent.
Good luck!