It’s a spacious apartment in a quiet environment. We were 4, and it’s good enough for 5 persons. You find everything you need (kitchen, two bathrooms, terrace, TV, equipment). The communication with Rui (at long distance) and Christina (on the place) was excellent. It was an amazing one week stay.
The beach is at 25–30 minutes of walking down the hill (we appreciated the "ocean swimming pool" at Estoril beach). The water is a little cold, but our children enjoyed it (end August). The best supermarket is ALDI (10 minutes up the hill). You can reach easily Lisbon by train (it goes often and is cheap - 2,20 euros). For other trips (Cabo da Roca...), we used often Uber (for 4 persons, it’s the same price as the public transport). We recommend to go to Lisbon (and specially to Belém), to Sintra, to Cabo da Roca, to Cascais. And we went also to Fátima (by bus from Lisbon).