We were 3 students from Switzerland and Germany studying in Seoul and spend 5 nights in SungJins house. We really loved the stay!
First the location: The beach is literally 10 meters away and the house and its garden are newly build and equipped with everything you need, from bathtub to a hammock.
The hosts: SungJin and his wife and kids were a real bonus to the already great impression of the house. They helped us with planning our trips, called taxis but also joined us to just talk and hang out, without ever being intrusive.
Additional Services: Things that might not be apparent in the advert: Even though the Guesthouse is listed as an Airbnb, there are always other guests living there who you can get in touch with in the daily dinner parties with self cooked, local food. These dinner parties also substituted the absence of nightlife in the sourroundings easily (beer and soju are available to buy for 2000Won in the guesthouse).
Another thing is, that the guesthouse seems to be far away from Jeju city and therefore activities. But SungJing offers to rent bikes, stand-up paddling, kite- and windsurfing and snorkeling. Therefore, this place suits to do more than just sleeping there and going to other places, as you can do different activities right there.
To summarize, this Airbnb is the perfect choice for people looking for beach activities or hang out in a family atmosphere out of the city; and still a great choice for everybody due to the clean and cozy location.
Therefore I can give an unrestricted recommendation!