My best friend is a SALT. She's currently in a research post. From what I can can tell the job itself is fab, but the people she has worked with determine her enjoyment at work.
Her first degree was in English Language/Linguistics and then she did a further 2 years in SALT training.
The worst thing she finds I think is working on her own. When working in schools, she can spend entire days seeing no adult at all; just endless driving from school to school with a snatched cuppa in a staff room and lunch in the car. I guess it depends how you specialise.
Pay is roughly similiar to a teacher's I think, but research seems to pay more than practising.