I went to the Steiner school just outside Totnes and I must say I loved my time at school, I was very happy and country to what tottytrot says there was a very low turn over of children.
Yes some of the ideas are a little strange but IME very few people take it all 100% seriously.
When I went to school (I did my GCSEs 10 years ago) we took only 3 GCSEs, that wasn't an issue because when applied to college they took into account our teacher's recommendations and I went on to do A-levels in biology, maths, sociology, photography and chemistry. I then gained a degree in photogrpahy and worked as a photographer in the UK and Australia for 5 years (now I live in Sweden and work as a English teacher.) Most of the people from my class at school went on to university, I'd say around 80%.
As for SEN I am dyslexic and still managed to get a b in GCSE English lit/lang, my mum works as a SEN teacher at the steiner school in south Devon.
The only issue you may have is that there are very long waiting lists, I have a friend who had to send her kids to the Steiner school in Exeter because there were not enough spaces in the year her son would be going into. Friends from school have their little babies names down now, so even if you think you might want to send your child there in the future my advice is put their name down now!
I am expecting my first child in December and we will put his name down for Steiner daycare and Steiner school, it is easier here because Steiner schools are free (all Swedish schools are free) so there isn't a finacial consideration. I am really not a dreamy hippy, I have the opinion that I would send my child to a c of e school without fully believing that christ rose from death and so why not send my child to a Steiner school without fully believing what Rudolf Steiner said. My point is that I have experienced Steiner education and I trust it enough to think that it is good enough for my own child.
Lastly the teachers do not teach the children the thories behind Steiner education. When you read the books it can all be a "bit much" but day to day your child will be in a very caring, inspiring, nuturing enviroment.