Our experience with Sonder was a good one and we will book with them again.
The price was very fair and they paid for the Airbnb commission. I suppose is better to book directly through their app, so you can use the app with your user name and email, and not the one provided by Airbnb, they won't work together so you don't get to feel the Sonder experience all the way.
The room was great, it was a modern day hotel experience. After figuring out the app not having my trip, and calling customer service, I could manage to get an early check in. There are few lockers for storage, but not at all enough for all the building.
Lastly, the Flatiron unit is located in front and above bars and restaurants. We found that people tend to go to NYC to get drunk and scream at night at the top of their lungs. It was very hard to sleep with the noise from outside and a roar from inside the building. Only over the ear noise canceling headphones could mute it off. Ear plugs, provided, wouldn't do the trick.
It's strange a "hotel" with no front desk to try to change rooms or ask for help.
But as I said, the price, the unit and the location were great. We would do it again.