Daniel's a nice and generous guy, whose appartment is located in a quiet yet lively part of Friedrichshain and close to everything you need, including an excellent powerlifting gym (Berlin Strength), a weekend market, trendy bars, world-famous clubs, and various local gems. I would recommend Daniel's place for the following personality profile: a quiet, very clean and tidy individual who wants something low-key and doesn't need total privacy. This isn't for partiers, couples, or people looking to bring someone home at night. It's a good place for digital nomads and people who want quiet after a night out.
With that said, even a guy like me, who takes pride in keeping things clean, found myself walking on eggshells from time to time. I try to be careful with the things I do, and yet found myself mildly aggravating Daniel with small mistakes, such as putting the wrong piece of film plastic in the garbage rather than recycling. You'll also need to sit down when you pee, guys. As a North American, this is really unusual for me and took some time to adjust to - naturally, it's hard to undo this automatism right off the bat, so I sometimes accidentally did my business while standing up, which I don't think he was super impressed with. I felt kind of uneasy about all this. He found hairline fractures in the bathroom vanity and one of the kitchen stovetop burners (a burner I never used) and alleged that I was responsible for the cracks... even though I never used the burner in question, and couldn't identify the scratch/crack he was referring to. In short, this is the kind of apartment for someone who is careful and meticulous in the way they do things. If you don't fit that description, you're better off somewhere else.
Last thing - as someone else noted, none of the doors lock. The entire apartment uses sliding doors. So there's no real sense of privacy at all. I find it strange how this isn't mentioned outright in the ad, since it's a pretty big deal for people who highly value privacy. Ultimately, I felt like I was sharing a common space as opposed to renting a private room.
Various other perks:
Big comfy bed
Premium lamps on desk and bedside table
Big bedroom windows
Lots of bedroom space
Cool pivotable shaving mirror in the bathroom
Sodastream
High-end kitchen appliances and utensils
Everything is "premium" and top-notch