schlee welcome to the neighbourhood. Beckenham is a great place to live!
My DD has just started at another school close by so I don't have direct experience of Harris or Bromley Road but have friends with children at both and all are happy with their choices. There are some local concerns about Harris's ability (generally) to meet any special educational needs but again, it's too early for any of us to have direct experience of that.
What I would say is this, one of the school principals said at their Open Day last year that while the choices were important, actually, all the local schools are really very good, and all had challenges too. Therefore, don't worry too much if you don't get your first choice as you're not going to end up somewhere dreadful.
I have to say that I would have been delighted with any of our first three choices. I know people with children at Unicorn, Oak Lodge, Bromley Road, Harris, Balgowan, Marian Vian, Churchfields, Alexandra, Clare House and few schools in Penge and I don't know anyone who isn't happy.
we won't talk about secondary schools until we know more about planning applications
Best of luck - all of the above said, it's a stressful time! This time next year, you'll be worrying about lines for the school nativity instead 