The apartment itself is absolutely fine: it was clean, spacious and fitted with a small but perfectly functional kitchen area, complete with dish and clothes washer. And it's in a good location, close to the central train station.
However, the area is under heavy redevelopment, and a new towerblock is under construction less than 100 meters away. So the noise levels are high during the day, and they're still working on the foundations, so this is likely to continue through 2019 and possibly even 2020.
Another point is around check-in. The hotel does provide you with instructions for this, but these could be a bit clearer. The "security" room where you collect your keys is the first office on the right after you go through a door in the far corner of the courtyard (labelled "Monitoring"), not next to a little hair salon as the instructions imply.
Also, it would be good if the check-in instructions mentioned the security deposit: this has to be paid in cash, and you can choose to pay in PLN, EUR or USD. It would have been good to know about the EUR/USD options - I had to leave for the airport at 04:00, so didn't have any real use for the PLN the security guard gave back to me when I checked out.
However, overall, it was a good place to stay, and I'd consider staying there again!