My family and I (5 x adults, 1 x 18month infant) had a brilliant stay at Asier's place. Asier was quick to communicate beforehand and met us on arrival to his place. He was very thorough and helpful when going through the check in and provided a map and tips. The apartment was clean, provided a decent amount of crockery and cooking equipment for when we didn't eat out.
We really liked the location in Gros. Only a couple blocks from the surfing beach and a walk away (about 20-25mins walk) from the old town and La Concha Beach. You have a shop/conveniences for everything you could possibly need nearby - fruits and veg, bakery, gelato, supermarket, coffee shops, bar.
Parking is expensive in the area but Asier can arrange for one space at a slightly discounted price. Otherwise there is an underground carpark (Txofre) about 7mins walk away where you can speak to the people in the office and arrange for a multiday ticket that allows you to come and go as much as you please. We parked for 4 days at a cost of €66 or €16.50 a day. Expensive if you're not evening using the car as with us.
The only slightly negative thing to note is the noise that comes from the cafe/bar opposite and from the street. It's not too bad but I did need my earplugs to get to sleep a few nights.
All in all it was a real pleasure staying in Asier's place and I'd recommend it to anyone staying in San Sebastian that doesn't want to or is unable to stay in the Old Town. My family and I would be happy to stay there again.