It's a bit of a hot house, and wouldn't suit every child, but it does have a good reputation locally.
You will need to register and pay a deposit, and your child will sit an entrance exam in January of Yr 6.
It's selective, and I believe that they have practice paper examples on their website.
Regarding tutoring, a small amount of tutoring to familiarise your child with the question types/styles is a good idea. If intense tutoring is required for your child to make the grade, then it's probably not the best fit for your child, as they have been known to ask pupils who are struggling to keep up at school to leave.
It probably best suits a highly academic, confident child.
Other schools in the area that you may also want to look at include Caterham, Dunottar, Whitgift, Trinity, Royal Russell, Lingfield Notre Dame.
They're all different and would suit different children best. Probably worth visiting them and getting a feel as to where your child would be happiest.