My girlfriend and I stayed in Petr's flat for 4 night and could have not got anything better for this price range in Prague.
Location is perfect, on the outskirt of the new town and just 10 minutes away from the old town.
Everything is at walking distance and we never used public transport.
The flat and the room are very clean a d comfy, however situated in an old building not perfectly well kept.
If you are up to something clean, and in a good location go for it, if that is not enough and you are up to something fancy, get something somewhere else and more expensive.
I will be definitely be back.