I stayed at the single room, it is cozy and simple. Mary was responding very fast to all my emails and questions.
Ranellagh is a lovely area - lots of nice resteraunts, coffee and bakeries, still it is quiet and safe.
I walked to Dublin's center- a nice walk of about 30 minutes (the weather was perfect but you can use the bus also).
7 minutes walk to the Airport Bus station.
great value for the price.