All three of my children are at Heritage School so I'm well placed to comment! We absolutely love it and can't speak highly enough about it.
What you pay for at Heritage is something very different to other day schools so you have to be comfortable with that. You're not paying for the astroturfs and amazing dining halls that St Faith's offer. But a very specific pedagogy that privileges nurturing children's curiosity in ways that I didn't observe when we looked around other schools. A focus on nature (weekly nature walks, forest school), poetry, handicraft, history taught chronologically so they know where things slot in, children offered a 'feast of real books', and narration. Children are taught to be able to narrate back what the teachers have taught, growing their confidence in public speaking, and any examination in the lower years is done orally, with a view that being able to articulate something is what shows understanding.
You won't get yoga, but you will get latin, poetry recitation, French from the very lowest years - a traditional education.
Heritage children have the most extraordinary knowledge of the natural world - my older son knows things I was never taught about the birds and berries and nesting animals of Coe Fen. After stomping around looking for these things, they go back and draw amazing line drawings of their findings in black fineliner pen. Then they'll write poems about them, or study a composer who wrote music about them.
Sports - like many of the private schools, Heritage uses the facilities at the Leys. I wouldn't say that it's the sportiest school. My children aren't the sportiest (more into drama and the arts) so this is fine, but if you want the old-school prep school sports experience you're better off with the Perse prep.
Religion - we and most of the families in our class are not practising Christians. It is true that the school has a strong Christian ethos, but we appreciate that Bible stories are also taught for their cultural currency.
We looked at Sancton Wood too and it struck us as just extremely 'cosy', which wasn't what we wanted. Yes Heritage is nurturing, but SW seemed to be kitted out very much for special needs children and those who weren't fitting in elsewhere (which they were brilliant at there, but it wasn't for us).
Heritage in many ways is the antidote to independent schools. It's positively trying to offer something that the others aren't - and that's either something you want or not. You're not paying for access to a cliquey monied set, but an approach to education. Academics are prized, but the route to getting their is never at the expense of the child and mental health. And strangely enough, while there is none of the hothousing that you find at Kings, you'll find that Heritage children still end up benchmarked several years above the national average. Funny that! I guess it's self-selecting in that a large proportion of the children have academics as parents. But the small classes (much smaller than St Faiths, for example) and very individualised teaching means that they can help every child reach their potential without giving them a nervous breakdown and masses of homework every night.
We liked the price-tag too - half that of some of the others.
I could go on - I think every Heritage parent you speak to will just wax lyrical about it. It really is a very special school indeed!