We really enjoyed our stay in Testaccio. Marco's flat was very well provided and he gave us a warm welcome with lots of useful information about the area, transport links etc, and was very helpful. The flat is spacious and quiet, Kitchen is smallish - but fine for three of us. Good bathrooms and laundry facilities. And it was all spotlessly clean.
We liked Testaccio very much -relaxed and friendly, great for food - Linnari cafe, da Remo, Volpeti Deli - where you get to taste everything before you buy, and especially Flavio al Valvevodetto trattoria set into Testaccio mound itself. It's easy to buy delicious food locally to eat at home - and that does't involve much or any cooking - if you don't want to eat out every evening.
We asked Marco to book a taxi to pick us up and return us to the airport, as we didn't want to have to deal with public transport with suitcases - this worked very well, cost 50 euros each way. For us the convenience and lack of stress of doing it this way was worth the the extra cost.
We walked direct to Forum area in about 30 minutes, otherwise took buses to centre, and in fact didn't bother with buying day travel passes as this wouldn't have been cost effective for us. We also used the wifi dongle Marco provided - and for 15 euros this was good value.
If you can't face the crowds of the big tourist areas every day there's lots to see and do in Testataccio itself, whether wandering along the Aurelian walls or Caracalla Baths, eating gelati in the park or enjoying local nightlife. Only regret is that I didnt get a chance to visit the bookshop/cafe/club that opens on weekend evenings on the corner of the square 30 seconds fm Casa Testaccio.
Overall, Casa Testaccio a very lovely and atmospheric place to stay.