I have stayed at Karim's place for 5 nights. If to say about the price/quality rotation, I must say this place is a very good choice. Good location, nice old typical Parisian appartment with nice cafes around. Even though Karim wrote couple days prior the trip that he is not in the city to meet me and explain everything on spot, his instructions are good enough to follow and find out everything by yourself.
My only notes are about the door in the shower in not the perfect working condition which brought some inconveniences and very thin walls that you hear all the neighbours and next door steps. But the second thing is, of course, just the fact of the inner layout of the building. My overall impression is good anyway.