Our stay at Kostas was not as enjoyable as you might read in most of the reviews here. However, to give credit where it is due, it's important to point out that Kostas himself is a warm and personable host who responded promptly to most messages we sent. Wouldn't likely recommend this stay to others, reasons as follows:
Pros:
The apartment is spacious, located centrally in a nice area of town, and has a great balcony with nice sea view and plenty of space inside and out. The place itself was older but clean overall.
Cons:
Despite having read in other reviews that previous guests had been received by Kostas at the port, and despite notifying him in advance of our arrival (including what time and what boat we would be coming in on), we were asked to find our own way to the apartment. Not too bad if you're fit, but we had expected better, and had to truck along our suitcases down cobblestone roads for about 15 minutes in the mid-day sun, with limited and no sidewalks to get there. Only reason I mention this is because it was in contrast to the other islands we had stayed at, where we had been received by our hosts at the port, no questions asked.
On arrival, being familiar with older hot water systems in Greece, we specifically asked our host if we needed to activate the breaker switch in advance of showering, or do anything to ensure the availability of hot water. The answer was "no". On the first day, we had decently warm water, enough for one shower of two. Naively, we hoped that things would improve over the coming days, however the hot water availability worsened to the point where the showers were lukewarm for 1-2 minutes, then simply cold thereafter. We tried running the tap/shower for lengthy periods of time on both hot and cold, at different times of day, etc. Normally the warm water would just fade away even though you had maxed out the faucet to the hottest setting. Kostas did mention at the end of our stay that he could have attempted to fix the water heater if he had been informed sooner. Just be aware there may be some issues, and all the units were full with guests at the time.
The WiFi connection was not working when we arrived, and we addressed it with Kostas within the first hour. He was able to replace the modem within about 24 hours time, which was reasonable for anybody having to make a repair like that on short notice. Unfortunately this limited our ability to plan our first couple hours and next day in Naxos, and it was preventable with a regular function check (other reviewers had mentioned the problem, as we later discovered by reading older reviews).
A couple other irritants were experienced throught the stay, such as having to ask the host for more toilet paper (we were given half of one roll at the beginning of our stay, and no extras were stored in the unit), and having to run to a supermarket as the shower was only equipped with conditioner (no soap and no shampoo provided, in contrast to all other Airbnb's).
Although previous guests reviews had indicated that their rooms were checked or turned down in some form each day, our bed was made and towels were changed only incidentally, once we had made a request to Kostas, asking for a new roll of toilet paper. Was it a big deal? No, but it was annoying and something that we didn't really want to deal with on vacation. Additionally, no paper towel in the kitchen and a single dish cloth. Simple stuff that you don't want to deal with while traveling and are paying good money to stay.
Significant issues with bed comfort and perpetual street noise at night (constant honking cars and motos, people yelling to eachother, and very loud exhausts from powerful motorcycles flying by every half-hour).
We rented the unit off the good reviews we had read, of which there are many. However, when I went back into the reviews (after experiencing some of the issues we did) I was able to find a couple reviewers with a nearly identical experience to ours. Having already visited several other locations in Greece (AirBnb), this experience was more irritating in that we had to ask for everything, and little was provided unless you asked.