The apartment is nice, the location is good and the host responsive. There is a very basic gym but during our stay, the treadmill was mostly out of order.
As to the apt, it is pretty spacious for a 1 room flat. It is well equipped: bed, couch, big tv and the kitchen comes with almost everything you need except a knife to cut vegetables/ meat. One of the kitchen stools is broken (you cannot adjust the height permanently). Bed and couch are notably used (mattress and cushion gave way) so that they were not really comfortable, though this is probably our personal issue and might not affect other people. Sometimes in winter, it gets a little cold in the apt but there is no heating or at least the host did not tell us about it.
The location is pretty sweet. A supermarket, some nice cafés, a market and parilla peña (steak restaurant) are in easy walking distance. You can actually also walk to Palermo, Recoleta, Puerto Madero (40min + -), but if you dont want to, the public transport service is good.
The host responded to our requests even though we would have wished for a quicker connection. That might have been our fault as well. If you want something taken care of, also explicitly indicate how fast you would like it to be done. We e.g. ran out of toilet paper and asked for it for the next day. We left it to the host when he finds the time. Eventually he only brought it at 10 pm.
All in all, our issues were minor and we still had a decent stay. Recommended.