My DD moved there in yr5 and this did make for a smoother transition to senior school. That said, they go out of their way to welcome new pupils (she had a handwritten letter from one of the girls in her class before she started and had a getting to know everyone day too). If you are not already paying for a private school, I would say save your money and move in Yr6 or wait until seniors.
The amount of girls is lower as it was originally a boy school and Coloma attracts many local girls, but it is rising. Girls have been encouraged to stay on and they are getting closer to equal numbers year on year. The small class sizes are a plus! That's what you are paying for and certainly helps in terms of staff knowing your child. DDs classes are 19 and 18 respectively I think.
Pastoral care is good. We had a minor bullying issue which was stamped out immediately we were aware of it and we were kept informed throughout. I know of parents of children with learning support needs and they have been very happy with how this has been managed.
It is of course a small school, compared to the state secondaries in the area and as such the facilities are lesser, but they make good use of what they have and use outside facilities such as Norman Park and HSBC sports ground.
There is an open day coming up soon, so why not go and have a look around? Take your Ds and DD with you and see how they react. Ours acted like she was totoally at home there, so made the decision for us in a way. We do sometimes wonder if she would get more from a large academy, but I think she might also get lost.
HTH