We stayed one month at Juan & Josephina's place and it could not have been better. We loved the place and felt at home.
Everything is as described. Balvanera is a quiet neighborhood with plenty of small markets and grocery stores. Located between the Subte stations Venezuela & Jujuy it takes between 15 minutes to reach Ricoleta and San Telmo and 30 minutes for Palermo and Boca.
The place itself is an architect design house which means very well decorated and very bright as well. There are two patios, a big living room and a dining room which allow all flatmates to have their own space even if everyone is at home. Also, the kitchen has everything you need to cook big dishes.
Finally, Juan & Josephina are the sweetest hosts ; always ready to help you have the greatest stay.