As a disclaimer, be aware I was here during high summer (mid August). Things are apparently very different during that time. Not just the heat (and there was a lot of heat) but also many (most?) of the locals are gone.
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TLDR: The place itself has a few small problems, but overall wonderful. However, at least during high summer the buses and trams aren't even close to on schedule and that really made it hard to get places.
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The place itself was clean and "IKEA-nice". The main bed wasn't great (memory foam with too much memory). But everything else was was up to or exceeded expectations in the place itself. Plenty of room to put away your stuff. I had the place to myself, but with 2 or even 3 people it would have been fine. It was certainly more than I needed, but it was welcome. Plenty of dishes to cook with. A bit short on some of the dishes I'd like to have (only one larger glass, only one bowl). But plenty of everything else.
I didn't use the patio as much as I should have. It's huge and wonderful. Could use a bit more shade I guess, but it was crazy hot when I was there, so I was only out after the sun was down anyways. But I liked having it for certain.
As a suburban-living American, I initially felt the neighborhood wasn't the best. But I was there for a week and by the end I found it to be just fine. Simply Market is where I'd do any serious grocery shopping (as the hosts recommended). All told I loved the neighborhood and walked it a fair bit. I felt safe even at night. I found it interesting that during the time I was there (again, high summer) lots of restaurants didn't really open until 8pm or so. Some weren't open at all, and some didn't serve real food until then. I imagine this is different during the colder parts of the year.
I was really worried about the heat without AC. It was in the high 90s a lot when I was there. But I shut down the house during the day (closed all windows and shutters) and the apartment stayed fairly cool. I did need to go buy a fan. But once I had that the apartment was fine even when it was 99 outside. Before I had the fan it was too much.
The apartment really does shut down. At one point a car alarm was going off just outside the room (the only noise problem I encountered btw). I had just one window open. I closed that window and I thought for a moment the alarm had stopped at the same time. But if I strained I could still hear it. I wish my house were that sound (and heat) resistant.
So, any big problems? The hosts were a bit slow to respond, but nothing that caused any problems. The lack of a fan was a huge problem given the heat, but easily fixed (and hopefully now fixed for anyone else who comes).
But the only reason I'd probably not stay there in the future is the distance from the touristy parts of Rome (which is where I went mostly). The buses and trams, at least during the high-summer, just don't hold to a regular schedule. The Metro and trains do. I waited 40+ minutes some times. I literally saw 4 trams go the other way before one came my way (a bus I could take came by so I grabbed that and so never saw one going my way after ~40 minutes). If you are going to be here and want to be in tourist-Rome, you need to figure out *all* the buses you can take to get to where you want to be. Bus H is the best one, but others can get you close. And one time bus H when I was at Termini station just didn't run. The bus drivers couldn't help. At 40 minutes, I just walked to the Tram station (a bit less than a mile) because it wasn't clear there would ever be a bus. No one had a clue what was going on. Now in fairness, the public transportation system is remarkably cheap. Be sure you read about how to use it. But I had a one week ticket and it got me everywhere inside of Rome I wanted to go for 24 Euros. Much cheaper than anything else I'd seen in Amsterdam or Paris.
That said, if you aren't relying on public transportation, the place is a great deal. I loved being there. Nice, clean, and a joy to be living in a place where I was one of the very very few tourists. A good way to see the "real Rome". If buses and trams were more reliable (and they may well be outside of high summer) it would be just about perfect.