I've stayed 30 days at Karina and Walter's apartment and I can guarantee that they were great hosts!
The apartment is clean and super well located: you have 2 subway lines 2 blocks away and several bus lines too. There is one market on the same block and another one across the street.
The air conditioner will do the trick to keep you warm during winter. And the shower can get pretty hot too.
I was staying with a friend and we both were working from home having several meetings throughout the day: the internet worked fine.
The kitchen is super small, so it's complicated for long stays: we ended up eating outside almost every day. But it's good enough for making coffee or simple dishes.
I would definitely stay there again, especially if I was on vacation, just enjoying Buenos Aires.