I stayed there for two nights in mid-December, 2019; it was my second time using Airbnb. I had actually already stayed at a B&B (not Airbnb) in Sintra for a few nights earlier in that trip, but I decided to extend my stay in Portugal a bit while I was there and ended up coming back to the town (yup, loved it that much).
Compared to my previous accommodation, which was closer to the historic center/National Palace, I can say that this was definitely a much better choice of location. It's still within walking distance to the historic center (at least for me), especially given that Sintra is such a pleasant place to walk in, but it's also close to the supermarkets and more reasonably priced restaurants in the Portela de Sintra area. While deciding on an accommodation, be aware that there are virtually no markets or places to buy basic necessities around the historic center, and, since it's a highly touristy place, the restaurants there are mostly on the expensive side with some tourist traps, so if, like me, you prefer self-catering and having more affordable restaurant options, the area around the train station is a logistically better choice, while still preserving the magical Sintra atmosphere which Portela itself lacks.
If you want to eat well rather than cheap, though, there are also some very good restaurants right next to the station, even better than most in the center, I'd say - Incomum is my personal suggestion, from experience, though I heard Metamorphosis is excellent as well. (There's a list of restaurant suggestions in the living room.)
The proximity to the train station also meant I could walk from there to the place in maybe 5 minutes, even with two pieces of luggage, one of them heavy, with no need for a cab. Note that there ARE steps between the street and the front door, though, but host Francis kindly helped me carry my luggage to the front door. The apartment itself is entirely at ground level, i.e., no more stairs after the ones outside.
There is the issue of hearing the noise of the trains, as has been mentioned and as should be expected when staying close to a station - there are a few every hour, from 6 AM to 1 AM, everyday -, but at that distance it wasn't overly loud to me, and, since I'm in the habit of sleeping with earplugs everywhere, even at home (busy street right outside my window), that didn't disturb my sleep at all. Compared to the advantages of the location, it felt like a small price to pay, but I thought I should comment on this, in case it's a dealbreaker for other people.
The place itself is really spacious, more than I expected, which I believe would make it comfortable for a longer stay or for a larger group. The living room is quite large, with a huge table, sofas and armchairs, and loads of power outlets, as well as a wall heater. There are three bedrooms, made available according to the number of guests, as explained by the hosts in the description. Both the bathroom in the suite and the one in the corridor have both showers and tubs. The corridor bathroom is right in front of the two other rooms, which is convenient. There's also a super well-equipped kitchen; if I'm not mistaken, it included a dishwasher, an oven and even a washing machine. My stay was short and it was my last stop before going back home (i.e., no point doing laundry then), so I didn't really need those, but I sure wished the places where I stayed longer had all that!
I was alone, so I only used the suite and can't comment on the other rooms. There's plenty of storage space in the suite, between the large wardrobe and the chest of drawers. The mattress and pillows are comfortable. Note that only one side of the bed had a bedside table. I missed having a power outlet in the bathroom - just a small issue for me, but I suppose it could be a problem if you use hair dryers, straighteners and the like.
Since it was late fall and rather chilly, I brought the other, portable heater in the living room to my bedroom, which was enough for me. I'm not sure whether there are heaters in the two smaller rooms, so if you're coming in the fall/winter and planning on using more than one room I'd advise you to ask - at least if the people in your group are as sensitive to the cold as I am (born and raised in the tropics!). There were warm blankets in the wardrobe, though.
The terrace offered a delightful view of a street lined with fall-colored trees, Christmas lights and some quaint buildings. If you prefer more monumental sights, look up to your left and you'll easily spot the Moorish Castle; it's all lit up at night.
The hosts live in the apartment right in front of this one and are very responsive to messages, so they were super available any time I needed them. In fact, when I had a problem with my bedroom window blinds not closing, both hosts came over ASAP and it was fixed before it could become a disturbance to my sleep (a room change was also offered in case it couldn't be fixed).
Overall, I was really pleased with my stay. I would stay there again and would recommend the place to friends and family. Thanks to both Izumi and Francis for being such good hosts and providing such a good and affordable choice in Sintra.