Can't comment on Rose Hill, but we had three children at Marple Hall between about 1993 and 2006. So like Admin, we're a bit out of date, but not much!
As at any school, you get the luck of the draw with teaching - there are (or were) many really good teachers, and also a few others who seemed less effective (or putting it more kindly - whose teaching styles did not suit our offspring!). But our three did well, got good GCSEs and went on to do A levels and to get good degrees: two 1sts and one 2(i). More important (IMO), they were happy there, and came out well-rounded and well-socialised.
I think you are right to look ahead to secondary education, as if your children go to Rose Hill they will almost certainly want to stay with their mates when they go on to secondary school.
Ofsted reports can be useful, but personally I would not place too much confidence in them. Ofsted has its own agenda and its own priorities, and these may not be the same as yours!