The check-in process was easy. We were met at the door when we arrived. Until we did, Petr and the person actually meeting us there were very responsive to messages we sent them.
The apartment itself is very spacious. At the end of the day, everyone who needed a little space to themselves was able to find some. The table in the kitchen is large enough for everyone to eat at together. The showers had good pressure.
The only thing I took off a star for was the location. It's not in the middle of the Old Town, so if you're going there, it's always a walk or a tram ride. That said, it's not a far walk, and the trams are excellent. (Recommended to figure out the routes and pricing in advance. You can buy tickets with contactless credit-card on the trams.) The apartment is one flight up and faces the street. However, even though there's a bar next door, we were not disturbed by any street noise.
The only downside to the apartment is that the wifi wasn't good (August 2022). Slow, and the connection would drop a lot. Usable, but frustrating (especially as there were six of us). As this is the kind of thing which is likely to improve over time, if this is an important factor I'd suggest asking the host if it's been addressed before booking.