I stayed for 10 nights so can vouch for quite a lot, I'll try to break it down so it's more helpful.
Summary/TLDR:
Very clean, very comfortable, well priced, great shower, great location!
Communication/Meet and greet:
Very good, met easily at the Calzedonia store which is round the corner and will likely become a point of reference for you and to meet people in the area. It's straight down the road from Fabrika (AKA South Bus Terminal) so very easy to find once you're dropped off. FYI, Taxi there cost me 15 Euros.
Location:
Unsurprisingly, very, very good. Most of what you'll do from a sight seeing perspective is in and around the area and if you're motivated enough to do a sunrise at the windmills, you've only got to walk for 2 minutes! Despite being so central, the street is quiet and I wasn't disturbed at all. If the early morning light wakes/disturbs you, consider closing the shutters, but noise isn't such an issue.
You're also super close to a whole host of restaurants or varying costs, if you want a cheap eat you cannot go wrong with a 4 Euro gyro from Jimmy's around the corner!
As above, you're also very close to Fabrika making most of the main beaches not much more than a 10 minute bus ride away, if that.
The room:
Whilst it's not large, per se, it's absolutely fine and whilst I stayed alone, I don't think a couple would have any trouble. There's a spot for one large luggage item under the safe and so on and if you had another that could go near to the bed without creating inconvenience. The bed is large and very comfortable. The shower is also well sized, not a little box, but powerful with good temperature control, it also has a detachable/hand shower head if you prefer that to the overhead shower head. There's also a Nespresso coffee pod machine, but I'm not clear on who provides the pods. Just don't get the Illy ones that I found, they won't fit!
Cleanliness:
Fantastic, room was cleaned every day which surprised me! Bed made up, fresh towels, the lot. Can't be faulted.
Value:
Mykonos is not a cheap place to visit so all things considered above, I think the apartment represents great value, especially so if you're staying as a duo/couple.