The location was great (Sintra has so much to offer!) and the flat was very clean, but that's about it. It was cold, damp and extremely unpleasant to stay at. There were no portable radiators and the ac/heating system was pretty useless. Also you can only use about 3 appliances at a time, so the power would cut out if you wanted to use the heater and hairdryer at the same time.
I think we would have had a better experience if we stayed in summer - but I do not recommend this place in winter months.