A great stay with great hosts! John was very proactive in communicating with me, self check-in was simple, and the neighborhood is super quiet with terrific scenery. As a solo traveler I found the apartment space to be big and quite cozy, and the desk area was great for working from "home" and taking video calls when needed. The shower heats up quickly and the duvet in the bedroom was also very warm, which I really appreciated since I was staying here during the coldest part of the year in Seattle. Parking on the street in front of the house was always available. If you're comfortable with a half-mile uphill walk from the house you can also catch a bus to easily get to central Ballard, downtown Seattle, or the UW campus.
While the host's family does live upstairs and you will hear footsteps and the occasional sound of a vacuum above, I rarely heard any voices or other sounds during my month-long stay. The listing mentions that they installed soundproofing in the ceiling of the basement apartment, and that seems to be quite effective.
If you choose to stay here, do be aware of the two sets of outside stairs that the host mentions in the listing. There are no handrails, the concrete could of course be wet from rain, and if it's after dark you may find a couple spots where the walkway is dimly lit until one of the motion-sensor lights comes on. This was not a problem for me, but may be a consideration for others with mobility issues.
Lastly, take advantage of the private beach access if you can! This does require a little bit of planning to ensure the tide is low enough, and also involves two sets of stairs and crossing the railroad tracks to get down to the beach, but once you've arrived it's a wonderful location. This stretch of beach is much more quiet than the public beach accesses at Golden Gardens or Carkeek Park, with all the same amazing westward-looking views. It's a great place to see a sunset.
I would absolutely stay here again. Thank you so much, John!