We had a great 4-day stay at Ibon's. He takes meticulous care of the apartment, keeping it very clean. It is in a very convenient location which is about a 15 minute walk from the center of town (where all the pintxos bars are) and a quick walk to the nearest beach (the surf beach).
There are 3 bedrooms available for guests - 2 have windows looking out to the street and the other - which we stayed in - just has one which looks out into a shaft where tenants of the building hang their laundry so you don't get much sunlight. There are also two full, very nice bathrooms in the space. There is no A/C but our room had a small fan which kept things comfortable.
Ibon is a very nice guy and responsive. His english is limited but we were able to communicate easily enough.
Overall a great space and a good choice in San Sebastien.