We stayed in the apartment for 5 days (7 students). The apartment is pretty big and the two bathrooms are spacious. The best thing for us was the big balcony, which included a great lounge for chilling out after the beach.
The welcome from Frank was perfect, he showed us everything and gave us also a map and some information about bike rentals and where to go.
The location of the apartment is right behind the beach, there are some delicious tapas bars right next to the building. If your main interest in Valencia is also the beach and not just the old town, then it's the perfect location. There is a metro station within walking distance (3 minutes) which leads directly to the old town "barrio del Carmen" (ride takes about 20 minutes). The beach is very big and pretty clean. There are some great restaurants, clubs and bars right at the harbor (5 minutes walking distance).
We enjoyed our stay in the apartment and we would definitely recommend it :)