We had a great time here!
It's a bit further out of the centre, but not too much IMO. There are nice restaurants and other amenities around. You might need to walk a bit to reach public transportation, depends on where you go, some buses are only a few minutes away and even the subway is only around 8-10 minutes, but note that on the way back you need to walk upwards.
Regarding sightseeing Park Güell is only 10 minutes, La Sagrada Familia around 20 on foot, for others you probably need public transportation.
Alex is a great host. He welcomed us personally and took the time to show around the apartment and to let us know where are grocery shops, pharmacies, etc. nearby. He is easy to communicate with and open for questions.
The apartment doesn't have TV (but you are probably not there to watch TV anyways), but does have AC, washing machine (can come handy) and dishwasher (unfortunately we couldn't use it, but it's only a one off occasion). Also a kitchen equipped enough.
Depending on your needs this can be a good accommodation for your stay. I recommend.