Overall impression: the stay was excellent in terms of location, really comfortable to check-in and check-out. There were no issues during our 4 days stay, so I can strongly recommend the place. Apart from that, I should say that Arek is a super-host indeed - he really cares, and he is ready to help and advise.
Apartment: that was super clean and causy, with a stylish and handy furniture of a high quality. There's enough space for a small company if you want to spend a warm evening with a coffee. The kitchen is more than enough for cooking purposes, the bathroom is spacious and neat.
Surroundings: quite a safe place with a packed night life (if you need that), modern shops, caffees and expositions, and surprisingly quiet!
For those who need to work during the stay (like me), please be aware that the internet connection is good enough, though might not work stable 100% of the time. FYI there're a couple of very convenient places to work within the flat - shouldn't be worried about that.
For those who are planning to stay longer than a couple of days: the flat is on the -1 floor which means it's pretty dark inside most of the time. If you're okay with the lack of light, then it's perfect for you.
Arek, thank you once again for your assistance and your place!