The future is not as bright as it appears you think it will be.
On November 4th, 2016, I was made redundant, I knew it was coming and spent a lot of time (seriously, a lot, I had been 32 years in a desk-bound job) researching my future prospects. I decided that becoming an electrician would be a change, a chance to do something practical, and would be as lucrative as my previous job. I did a 16 week course with TradeSkills4U, I felt the course was comprehensive, well structured, and, at the end I had all of the qualifications to get my NVQ 3, and call myself an electrician - apart from the experience. I'm working toward the experience now, and it's going to take a while - I'm 9 months into what I think is going to be 3 years getting enough experience to be able to complete my NVQ 3 and only then be able to call myself an electrician. In the mean time I'm being paid as a labourer, and that doesn't pay what I'm used to. My redundancy is diminishing, it may not last the remainder of the three years.
You're talking about Domestic Installer, from my experience it's a job title looked down upon by electricians, you won't be an electrician and you'll be competing with people who know so much more than you, and have skills you'll never develop due to not having exposure to certain aspects of the job. From reading here, and talking to colleague sparks, as a Domestic Installers your best prospect will be to find employment with a kitchen fitting company, your prospects as self employed are virtually nil.
All of these companies offering courses are out to make money. Yes, you can get where you want to be, but the work involved is much, much, much more than these training companies will have you believe.
Have your eyes wide open before you commit yourself to anything.