Marco's flat is pretty awesome. The big selling point for us was that it's built against actual Roman walls that date back to something like 279AD, but the rest of the flat is lovely - it's very modern and Marco has clearly put a lot of thought and effort into revamping it, with LCD lights and a foldaway kitchen.
The location is just outside the center - 10 minutes walk to the Colosseum and three minutes walk to the nearest Metro station. The location is also good for little local supermarkets, chemists and some small restaurants and wine bars (our favourite was Devin Ostilia on Via Ostilia) that are populated by locals rather than tourists.
Marco's flat was equipped and ready to go with wine and beer in the fridge and coffee capsules for the Nespresso machine in the kitchen. There were supplies for the washing machine and dishwasher. He also provided us with a portable wireless hotspot (the flat has wi-fi but Rome itself is a bit hit and miss), a mobile phone in case we needed a local number and tickets for the metro that we could use on an honour system - we just needed to replace them. He also checked during our stay to make sure we were okay and meeting us late in the evening to check us in was no trouble! We would both highly recommend Marco's place!