We just slept here one night and had a lovely stay. The only thing that stopped me giving it five stars is that you cannot close one of the bedroom doors because there is something wrong with the hinges.
But other than this it is an amazing flat - very spacious - apparently it was used to house Communism lecturers at the adjoining Institiute of Marxism until 1989, after which it became a broadcasting outlet of CIA-sponsored propaganda machine, RadioFreeEurope. All the interior doors remain padded/soundproofed from this era.
Although the busy street it is on is not very attractive, you are literally two minutes walk from the Old Town, by going under a subway.
The owner, Katarina, is lovely and was there within 10 minutes to let us in after we rang to say we'd arrived. She made sure we had everything we needed and helped us with our luggage and so on. Email communication prior to our arrival was really straightforward and her English is excellent.
I would highly recommend this accommodation to anyone visiting the city and if the owner can get the bedroom door fixed I'd have no hesitation in giving it 5 stars.