We only stayed one night at Vivis apartment, but it was a really nice experience for a short stay! The check in was also really smooth, and Vivi was very nice. The apartment was very roomy, with a beautiful big balcony, and right by the Kamari beach & center. Everything was near (for example, the shop right below is open until 2am). This apartment would be perfect for a family, or a couple like us. The kitchen was definitely meant for short stays though, and the AC unit was not great - it worked, but it took a long time to cool down, and it shut off when you took the key so the apartment was hot when you came back. Also it’s right by the airport, so you heard planes a lot.
But overall we would recommend this apartment for a trip to Santorini!