I like that it can be used by multiple users without having each user have their own copy of software, as well as how easy they make adding appointments very simple too! It doesn't seem customizable enough for our needs at this point in development though (we are working with one other person who uses another product).
So far we haven’t found anything negative about using cozycal so if your looking into an appointment scheduler then give them consideration. We use COZYCAL because its free compared to some others out there which makes us feel more comfortable giving access to employees across different locations/companies when needed due to security concerns regarding data privacy etc..