We only stayed one night at Stelios' place, but we had a great experience.
First of all the hosts are lovely and very helpful. We moved from another hotel on the island to Stelios' place early in the morning and even though check-in is only in the afternoon the hosts stored our luggage for us during the day. The next day we had some time before taking our ferry and spent it on the pool after check-out.
The room we had was nice. It is a cave-house like room, meaning that it is build into the ground, which keeps it nicely cool. The hotel is a bit away from the main touristic center and I would recommend having a car. We walked to Thera (ca. 35min), but a part of the road has no sidewalk.
As a side note: The next supermarket is ca 15 min walking away, but there are a lot of affordable delivery services available, whose flyer were provided by Stelios.
I can really recommend Stelios place, especially if you want a calm and relaxing location outside the tourist center.