I stayed for 2 weeks in august of 2014. Saniel picked me up at the airport and was extremely friendly and helpful. The apartment is located in a nice quiet area across the street from the Italian embassy. There are several restaurants and cafes located nearby and a main tram/bus station only 2 blocks away.
The unit is small, but has everything you need for a comfortable stay. The only negative is the couch/bed is not very comfortable, but this did not affect my stay. There are several small stores very nearby to stock the kitchen. Everything in the central city is within walking distance. If you need to use public transport Saniel has passes in the apartment for use and it's easy to find a kiosk to reload them. The wifi in the apartment is very good and reliable. One thing to note if you are from the US this is actually on the third floor as they count the first floor as 0 or ground floor. The building does have a working elevator. I did not hear a sound from anyone else in the building during my 2 weeks.
On one other note I would like to thank Saniel. I needed to get my white card and he went to the police station in new belgrade right away. When he called stating I needed to bring my passport I told him it would be some time as I was out to dinner with a friend. He waited two hours for me and made sure it was taken care of.
I would recommend staying here and add that Saniel is a wonderful host.