My partner and I very much enjoyed our stay at Marco's.
The main thing going for the apartment is undeniably its location - you couldn't be more in the thick of things than that! All tourist attractions/sights are very close by and it's easy to swing by the flat multiple times during the day to freshen up/take a little break/drop off any shopping etc.
The only minor drawback of the location is that is in a very lively part of a very lively street, so expect a degree of street noise! With windows closed, though, you're rather well insulated from the hubbub. If you're a light sleeper, however, I do recommend bringing earplugs to avoid both street and building-related noises (it's an old building with a rather loud lift and unavoidable noise generated by other residents coming and going).
The flat has everything that you might need during a short stay and is clean and reasonably cosy, although a quick heads-up: if you're not used to lack of daylight you might struggle to wake up in the morning! This is because there's no natural light coming in to the bedroom due to the only functioning window being in the living area and overlooking an internal courtyard. But it's hardly an inconvenience when you're on holiday and can take time starting your day!
The transit between the airport and the apartment is easy due to the coach stop being located mere 5 minutes' walk away and there's a multitude of very good food and drink options in the immediate vicinity.
The communication with Marco and assistance from his dad, as well as their willingness to accommodate your check-in/check-out needs is second to none.
Overall, I would definitely recommend Marco's apartment if you're visiting for a short visit and need an excellent, convenient location.