Stayed at Carlos's place for 3 weeks in October with my partner. The best thing about it is definitely the location. Pretty close to tons of cafes, restaurants, markets, etc. Metro is not too far away either. Definitely if you're looking for a central place to stick around Palermo it is great.
The internet was also great. Both of us worked from home and really had no issues with internet the entire time which was a super must-have. As for the apartment itself, it's okay but a bit small and when we were there really ONLY had the bare minimums and absolutely nothing else - like 2 forks, 1 bowl, 1 towel, etc. type deal. It has everything you need for a stay but definitely isn't the most well-equipped airbnb I've ever been to.
It is a studio so a bit small, definitely perfect for 1 person but doable for 2. I think for long-term stays I'd be meh on it but for under a month or shorter term, it's pretty good for what you get. Also, an important thing to note is the gym is like a 1 person at a time gym where you have to reserve. Also when we were there the sauna and pool were not working, but it was October so could be that - just worth nothing.