We stayed at Helios' place for 3 nights in December 2018. Location could not have been better for a tourist! We walked to most places to visit and nightlife areas. Taxis were readily available too when needed, metro station was a 5 min walk. There is a supermarket right across the street from where we bought our daily supply of water. Size of the studio is decent enough for 2 people. There are great bars and restaurants in the area if you don't feel like venturing far out.
As other reviews have mentioned, there is a club across the street and it can get very noisy on weekend nights. Party goes on till 4 am and closing the windows didn't help much. It was not a big problem for us as we had gone to Madrid to enjoy the nightlife more than anything else. But I can see it being an issue for folks looking to get some sleep.