Ruth's is a decent break from the monotony of not being able to find much vegan food in Florence. Florence is one of the nicest cities in the world, but that doesn't extend to vegetarian food.
As previous posters have stated, the owners and workers could be a bit nicer. The prices are fairly expensive, but on par with the normal price-gouging that is definitely ubiquitous in Italian restaurants.
The food is clean. I had the falafel plate and some pumpkin soup. The soup was excellent and seemed to be made from fresh pumpkins. The falafels were well made - as far as falafels go (I kind of hate falafels to be honest, because they are protein poor) - and they came with pita and hummus and tahini. It was good for what it was.
Ruth's is next to the Florence Synagogue which is worth a visit, costs €6 for entry, and has a museum upstairs.
Cons: Not cheap, Unfriendly owners / workers