Short summary: Tasty healthy food at a good price, large portions, but a little complicated to figure out if you are used to American restaurants. No cover charge (coperto)! Menu changes daily, making it a good place to eat every day. My favorite place in Florence.
The dish I ordered was two things. One one half was a mix of just random stuff: grapes, eggplant, black rice, red cabbage, etc. This tasted about like you'd expect: healthy, but not very exciting unless basic veggies get you excited. The other have was a seitan mixed with some sort of veggie patty-like mix, not sure what it was. That part was fabulous.
This is like school cafeteria. Go to the counter at the rear of the restaurant. If there is a line (all tables taken) then a waitress will assign you a table when one clears, but you don't site down yet. Order your food at the rear counter. Vegan items are clearly marked. You pay in advance. Pick up a tray and bring your order ticket to the food counter. Then they give you your food. Also don't forget to find the silverware tray to grab a fork a knife. Bring your tray to your table and enjoy!
Bring an Italian dictionary with you. This is not a tourist trap where everyone speaks fluent English. They know some English, but not perfectly. Menus is *NOT* written in English. But even if you can't read the menu, you could just point to some random item labeled "vegano" and see what you get.
Cons: Confusing setup for an American., Bring some basic Italian skills.