It is not less work in Secondary, far from it! I am in the process of swapping downwards the other way, so I know what i'm on about! I spent every night with a "task". GCSE and AS/A2 marking is increasingly onerous, and everything has to be levelled, just as it does in Primary. I had 1 Yr 7 class, 1 Yr 8, 2 Yr 9, and 1 GCSE, 1 As, and 1A2 class in my last year at Secondary, all of which required marking every week, in the school style, ready for spot book checks. AS/A2 essays were routinely upwards of 4 sides of A4. Then Christmas was spent readying for Mocks, Easter was spent in school doing revision sessions, after school from January to May I was scheduled at revision club, and then in the "off" time once the examinees had gone, we were used as cover or off site work experience checkers in our "free" periods.
Promotion also utterly depends on geographical area and subject. In mine, rural England, history teaching, it is "dead mens boots". More fluid when I was in London, of course.
Anyway, off topic. Tutoring being worthwhile depends on where you are. In London, I could do well, particularly with 11 plus candidates. But rurally, the charge is less and the 11 plus candidates fewer. I found that I had to travel into Cambridge to get enough uptake to make it worthwhile, and then the petrol wiped out a lot of it.
In the end, I went back as a HLTA, I do 8.30-3, have no childcare as the kids are at school with me, and no marking other than when i've covered a full day. It's lovely! And the wage is approximately what I made less childcare anyway, but with little stress and with the enjoyment of the job intact. I will consider going back, this time to primary, when I feel I can balance work and kids / life more easily. This isn't to say Primary teachers have it easy, they clearly do not, but the marking load was what killed me in Secondary, and that certainly is more manageable ( outside of Year 6, anyway).
I also found supply very on/off. It was nigh on impossible to balance it with childcare, and so last minute, unless the supply was for a teacher with a long-term illness, that it was just daft trying to juggle it.