Positives: we very much enjoyed our stay at Alex's place. We had a difficult time entering the building initially but Alex responded immediately and was very helpful. The location is awesome. Biarritz is fairly small anyway, but we liked how central the apartment felt.
Areas of improvement: a bit minor, but some amenities weren't up to par (e.g. there was practically no soap...again, very minor issue).
Other: as of the time of our stay, there was construction going on with the building next door, but given the location of the work, it sounded like it was next door - it was very, very loud. This was ok for the most part since we were primarily out exploring during the day but was super inconvenient when we were around the apartment or early in the morning.