All I know is there is quite a bit of social housing in Belarmine, more than the other estates and more is planned. It is very high density too, and may not hold its value well as other developments. I think there are better options in Stepaside away from Belarmine, Park View etc. at the moment.
If you are looking to buy new, look at Elmfield, although the address is Leopardstown its just down the road and closer to to the Luas stop. I know its more expensive but it is like everything else for a reason. I would imagine once the Luas is up and running these and all other properties within reasonable walking distance of the Luas stop will attract more attention.