My wife and I really liked the place from the moment we stepped in. Very clean, very modern and in an amazing location. We spent a lot of time exploring Balboa park, and we were able to walk there and back easily (~20 minutes from the apartment to the central museums).
The hosts were very courteous and were flexible regarding check-in, which was helpful because we drove there and had to fight through traffic the night we arrived.
We used street parking daily, and while the street was busy and there were a fair number of cars parked along it, we never had too much trouble finding a spot.
The bedroom was really nice - well maintained, had nice decor, and they added some thoughtful touches (towels and chocolates on the bed with a welcome note). The private en suite was impeccably clean, stocked with extra shampoo, conditioner, a blow drier, etc. The mattress was very firm (we're used to a soft bed, so it was a bit of adjustment for us). The bedding was soft and plenty comfortable.
Our hosts even had some fresh fruit for us and free Wi-Fi, which was much appreciated. I had to do some work remotely and although the Wi-Fi was a little spotty from time to time, I was able to get everything done that I needed.
We were extremely happy with our room and would highly recommend this place for your San Diego stay. We would definitely stay here again.