We stayed for 10 nights in late August / early September. 2 adults and 2 older teenagers and Luis place worked great for us. The other reviews are accurate so have a read of them for more info.
Things I would have like to have known, before:
Travel: For shorter trips, if there are 4 of you, use UBER its more convenient and cheaper. For longer trips get a Viva Viagem Card and load it with 10 euros each, then you can just Zap on all the forms of transport.
Sea is warmer end of Sept beginning of October.
Cascais was a nice place for a day trip on the train, cheap bikes opposite McDonalds provided by the council were fine and good fun. Can cycle safely all over. The Park in Cascais was gorgeous and the cycle route to Guincho Surf Beach was safe and not to strenuous.
Area is safe and we felt safe everywhere in Lisbon.
Local restaurants better in local streets close to apartment, than the more touristy areas.
Sintra - go on the train and the walk up is not as strenuous as is made out in the guide books., You can definitely walk down from Pena Palace and Moorish Castle and then visit the Quinta da Regaleira in the Town. These 3 are easy to do in one day, so get a 3 site ticket as you get a discount.
Other than that just wander the touristy areas and enjoy.
LX factory was a highlight then get an Uber bike to Belem along the river, about half an hour ride was 4 euros