I would definitely say I enjoyed my stay a lot at Erna's place. Not the most fancy place, but definitely of great value, and if you set the correct expectations, you'll be more than satisfied.
This is an old building in the city center of Sevilla, and there are (I believe) 12 rooms for guests, many of whom are there for long period. So things may be old, and it can get a bit loud at times, especially during holiday season (more about people shouting in streets). The long-time guests are great people and you probably want to get along with them - in fact if you do, you will really feel yourself at home. If you have questions, they will help you.
Everything is within walking distance. The house is well maintained, and the staff check in regularly. Checkin and communication are great. I slept well in general.
It's a fantastic experience and I have nothing to complain about.