I had a wonderful stay at Simon's place with my girlfriend. Everything was as good if not better than any other Airbnb I've ever stayed at, and Simon was quick to respond to any concerns or questions.
The location is excellent. The unit is situated on a quiet street far enough from the noise of central Manhattan but close enough to transport to get there conveniently. There are also plenty of attractions in the surrounding area, including but not limited to The Apollo, various jazz clubs and eateries, and supermarkets for any grocery shopping. We visited these places at various times of day and night and never had any issues in the area - exercise vigilance as you would anywhere and you will enjoy this part of Harlem.
The place itself is beautiful. Extremely spacious, with plenty of towels and linen and a ton of cookware should you prefer to prepare your own food. The bed is comfy, as is the couch in the living room, and the various snacks provided by Simon are a lovely gesture that adds to the homely feel of the place. As others have noted, the lighting is excellent as well - it's nice to be able to easily see what you're looking for. At night you may hear the odd siren, which for a light sleeper like myself can be frustrating, but it's nowhere near as bad as other parts of the city. I always carry earplugs so I didn't really have an issue.
Ultimately, the place is extremely well looked after, and Simon is great when it comes to communicating. I would gladly stay here again should I find myself in Harlem, as the place is great value for money and a pleasant change from the sometimes overwhelming atmosphere of other parts of the city.