Maria's Soul cave house is beautiful! It is exactly as described and has stunning views of the caldera, and easy access to the hotspots in Oia. Maria is an excellent host and made our stay very smooth, and her place offers excellent value!
Guests should be aware of two things when planning. 1) Access to any traditional homes in Oia is not straightforward. Maria coordinated with us on a place to meet, sent a porter to meet us there, the porter helpfully escorted us to a parking spot, and then helped with luggage over a ~10 minute walk with a good number of steps. We didn't think that was an issue at all, and Maria helped coordinate very well, but other guests should plan ahead and know what to expect.
2) As advertised, it is a traditional cave house. It is comfortable and has a small kitchenette etc., but it is fundamentally rustic. Guests should expect that there will be minor deviations versus fancier hotels (e.g., shower area and toilet have no separation, kitchen sink and bathroom sink are one and the same, etc.)