We had a nice stay. The flat is indeed small (although probably a good size for Paris), but very well organized and cozy. Plenty of natural light. It's not in a central area, but it's well connected and easy to get to main attractions. Lively area, plenty of bistros and cafes, shops&market, patisseries etc. Karla is very responsive and there were some nice touches (the bottles of water we found on arrival were greatly appreciated since it was a hot day).
It's slightly troublesome to take a shower since there's a big window right next to the tub and there are no blinds. There was unfortunately no space left/intended for our clothes and this was a bit of an inconvenience since we were there for 6 days. The apartment doesn't have air conditioning - this is clearly mentioned in the description and we didn't think it would be an issue since we visited in early September, however be advised that with high temperatures outside the flats gets very hot.