We just finished a fabulous weekend trip in Seville! Juanma y María were excellent hosts. María met us at the apartment. She was delightfully energetic and full of tips and information. She even helped me identify good GLUTEN FREE places in the city! She was also very prompt with her replies if I had any questions.
The apartment itself was ideally located for us, within 20 minutes walking distance of most things we wanted to see. If you're renting a car, do be aware that there is no immediate street parking. We arrived in the city during weekend rush hour and it was very stressful. We did end up parking at the Plaza de Armas, just a few blocks away. We kept the car there all weekend and it was a bit spendy at €23 per day. If you don't plan on driving around, skip the rental car and use public transportation or a cab.
The interior of the apt is a bit smaller than the photos depicted but we were really only in the apt long enough to sleep and drop off purchases so it wasn't an issue. I would say that if you don't like heights, aren't 100% confident on stairs or need to get up to use the bathroom a lot at night, that it might not be ideal for you. While they are secure, they are steep.
Also, as others noted, it is on a busy street. If you're a light sleeper, bring ear plugs. The standing fan helped block out some of the night time noise, however.
Overall, it was a very enjoyable stay. Juanma Y María were a joy to work with and their apartment was exactly what we needed for our short stay in Seville.