My friend used to work at Specsavers and really enjoyed it. I'm not sure what the pay was like, but when she started she did a two-day training course and the people she worked with were all supportive (she is visually impaired).
I worked at Vision Express for a few weeks, but hated it. Basically they didn't give me any training and on the first day just put me behind the counter and didn't tell me how to do anything. The other staff were always busy with other customers so I spent most of the time waiting for them to be free to ask them questions about what I was supposed to be doing. I left after I heard my boss saying not-very-nice things about me to another member of staff. I think if I'd known what I was doing it would have been a really good job - the things I did do I enjoyed, but the vibes I got of the other staff, especially the boss, weren't very nice so I found it really stressful.