I did not meet Fanis nor Tina, but their porter Tim helped out with check in (and check out), as well as with our bags. He was very attentive, knew the apartment well and provided good advice.
Communication with Fanis and Tina was easy and they helped with the transfer from and to the airport.
The place is AMAZING. It's got the view everyone wants to see. Very close to the main path, but yet quiet enough. During the day you need to elbow your way to or from the apartment, as lots of tourists are taking pictures, but because of a clever little door above the property, your terrace remains private.
The only regret I have is staying there only for two days - we had a lovely, relaxing time!
The cave house is comprised of a large room with the kitchen, dining and living room; a bathroom; the master bedroom. There's a separate room and a second bathroom which you can access from the front yard/terrace, so I would recommend it for two couples (it would allow sufficient privacy). Everything was VERY clean and decoration was just perfect. The yard has an amazing view of the Caldera (you can see all islands and the "cauldron"-like shape in the see) and of the rest of Oia, blue domes and castle ruins included.
I would recommend it, and hope to come back!