Juan Carlos is definitely a superhost and his apartment is simply fantastic for whatever length your stay may be (we were there for two full weeks and felt right at home). We never missed anything, the apartment is roomy and comfy, and the location is excellent -within walking distance to anything and everything that you may need, from a bakery to a brand new supermarket to the beach.
Mundaka is a great destination not only for a beach/surf vacation, but also to explore the Urdaibai Natural Park. Trains and buses run all the time (to Bermeo, Gernika and Bilbao, to name a few destinations) so you can park your car (if you drive here) and forget about it. BTW, parking in town is not easy, and you will not be able to drive right up to the apartment's door, but those are minor nuisances.
The apartment has all the appliances you may need and Netflix is available right on the TV (turn on and watch). Just note that the bedroom is downstairs, so keep that in mind in case you have mobility issues (permanent or temporary).