My fiancé and I had a mixed experience staying at the cave studio. When we arrived in Oia, we were told by a man Maria paid to pick us up that the studio we booked was unavailable because the hot water went out that day. It was a shock to be told we couldn't stay in the place we paid for upon arriving. Maria had the hot water fixed the next day and we were able to move into the cave studio but the experience left a bad taste in our mouths and distrustful of Maria.
The cave studio itself is lovely and just as described. The location and view are amazing. The bed is comfortable, and the shower has good water pressure.
One other note: Maria hires intermediaries to run this rental rather than helping guests herself, and we dealt with three of them in our short stay. We never met Maria. This isn't ideal. When staying at AirBnBs, my fiancé and I prefer to communicate directly with the property owners. It feels more personal and safe, and that the owner isn't simply running a hotel from a distance.