A very mixed review, this.
Firstly, the apartment is really nice: decent size, great location, clean.
But, during our stay, there were construction works taking place on the building. These ran from 8am to 5pm each day, and were really quite intrusive - drilling, sawing, banging throughout the day, with workmen walking back and forth on the scaffolding outside the sitting-room and 1 of the bedrooms.
And this is where our frustration crept in, and the reason for the low-star rating. We tried to contact Stay U-Nique about it midway through our stay: via email, and via WhatsApp. No response. We contacted them through Expedia messages, and they responded later that day, acknowledging the building works disruption - but advising that the works were detailed in the Expedia description. They weren't, and an Expedia representative confirmed they weren't. They didn't reply to my follow-up email.
I contacted Stay U-Nique 3 more times when we returned from Barcelona - again, I received no responses to any of those emails.
In the end, we took the issue up with Expedia - they also confirmed, after 'multiple attempts', that they didn't receive a response from Stay U-Nique either. Expedia ended up giving us a goodwill credit for the accommodation.
So, a decent apartment - and if you stay there when there's no building works, then you'll really enjoy it. But let down by Stay U-Nique's complete lack of response to any messages.