I had a great time in Diego's place. He was really helpful beforehand (asking if I needed 2 double-beds or 4 twins), and when we arrived his friend showed us around and explained everything we needed to know.
The location is excellent, just around the corner from the Uffizi and about 30 seconds from Ponte Vecchio, so it's easy to reach all the major sites - both North and South of the river.
Inside, the apartment had everything we needed. It's a converted vault or brick storage cellar (though on the ground floor), very well modernised and with a unique feel. Two bathrooms, two rooms and a kitchen/dining/lounge area. On the down-side there's not so much natural light and it can get a little stuffy (we visited in Feb and kept the window & doors closed!), but it's great for sleeping at night - no noise, no light. We spent our days & evenings out and about exploring the city so had no complaints about a lack of view, but look elsewhere if you want a balcony on which to sip morning coffee and look out on the world.
I'd definitely recommend staying here.