I'm an SLT (now working at band 7/ highly specialist after 8 years qualified) and I did my training on one of the Master's courses. The competition is really tough as the courses are NHS funded and you get a small bursary (or at least I did).
When I studied they wanted evidence of recent study and commitment if it meant a career change. I held down my full time job and volunteered for the Stroke Association on a weekend working with people who had language difficulties after a stroke, but even that wasn't enough when I applied so I also observed an SLT in paediatrics for a couple of days.#
However work shadowing is increasingly hard to come by, so
RCSLT often do 'taster days' for people interested in joining the profession so might be worth emailing them: RCSLT
Re becoming an assistant, contact your local SLT department and ask if there are any vacancies, or opportunities for observation days. They can be quite competitive too though; some Trusts (including mine) will sponsor employees who wish to go on to achieve qualified status so it's little suprise
Things I like (bearing in mind I work with adults): the variety - everyone's brain is different and so two patients with brain damage in the same place can present differently; and have different communication needs. Helping people to see how important the ability to communicate is. Meeting some truly amazing, brave, people and having the privelege of helping them come to terms with a major life change and the next phase of their life. It can be extremely rewarding.
Things I don't like: It's a relatively new profession (post war) and so there is a lot of rapid development and change in the ideas and theory of speech therapy as a 'science'. What you are doing in therapy one day, can be labelled 'ineffective' the next. The NHS as you will know isn't always a fun place to work. Older doctors will see you as a silly 'girl' with very little to contribute to patient care, because you are not the person that gets them back on their feet and out of a hospital bed. All hail the Physios and OT's
Was so demoralised by this I left to do a secondment for a year in an unrelated NHS job..but am going back in a couple of months with some much needed perspective.
Hope that's given you at least a bit more info to go by!