We had a great stay at Maria Teresa's place. I was there for work and my wife and 7-year old twins came with me. We stayed for a total of 7 weeks.
Location - Pretty much perfect in our view. If we do it again we will pick the same location. It's close to Spanish steps, but on a quiet street that is not full of tourists. There are tons of places close by to eat, both local and touristy. The more local places typically don't open for dinner until 7:30, so having some touristy places around, which are open pretty much all day, is great if you have young kids. The location is also close to a grocery store, dry cleaner, and whatever else you might need for a longer stay.
Apartment - Was very comfortable for us. We live in a decent sized house in the U.S., but the 4 of us were fine in the apartment for 7 weeks. It was quiet so we slept well. The kitchen was sufficient for simple meals. There is a washer and you can hang the cloths to dry, which works fine and is what most of the locals do.
Hostess - Maria Teresa is an excellent hostess. She promptly replies to all messages and is very pleasant to deal with. She arranged us airport transportation and gave us good restaurant recommendations. She even upgraded the Internet speed so our kids could do online classes.
All in all we would happily stay here again. Don't hesitate to book this apartment!