Positives: Location obviously (see below) and a quiet street (in August, Parisiens all on holiday), and with a carpark at the end of the road (St Germain des pres) which as we came by car was a big bonus). Communication was excellent and check in contactless and simple. The apart is nicely furnished and decorated.
Negatives: The lack of proper windows, there's a window that looks down into the entrance of a shop, so you can't really open it. So ventilation was an issue, it felt stuffy inside and it wasn't hot on Paris at that time. Not sure what it would be like in a heatwave, though there are fans. Also the apart is very small (always hard to tell from the photos). One of the bedrooms only has enough space for the bed, so you have to be agile if sleeping wall side. I wouldn't fancy sleeping 6 in this apartment. Also the pillows were bad (but they always are in ABnBs).
The wi-fi is good, the neighborhood feels very safe, and transport links from the apartment are excellent, also you can do a lot on foot from the apartment. We had trouble finding a bakery open nearby (August, nearest one about 5 minutes closed). Also, frustratingly didn't find the nearest grocery store until it was too late as didn't show up on a Google search (it's Monoprix btw, the apartment is above a frozen food store but no fresh food sold there). There are livelier neighbourhoods around, and not that many restaurants to choose from nearby.