Great apartment in a perfect central location - really close to the river, and just off a high street filled with high end retail stores and restaurants.
The apartment was very clean, comfortable, well equipped, and we felt very safe and secure. It had a unique mezzanine level, with the bedroom being located on a glass floor above the living area.
Mario's son Niccolo met us on arrival and was friendly and helpful - and the apartment contained a handbook with useful information about the apartment itself, nearby restaurants, taxi numbers etc.
The only possible downsides were that the ceiling is quite low in the bedroom area and the shower is quite small. But these were not major issues and I completely recommend this apartment - it was perfect for our stay in Florence!