I have tried many video calling app but Google Duo has given me the most pleasant experience.It is simple, fast and easy to use even for child.To get connected one just have to click on the App.Easy Contact view at the bottom and most exiting feature is call preview.
As for the data usage, there is option in setting to control data.As I have personally used it I think it cut more data than whatsapp video calling and less compared to facebook.
Overall for a richer and smoother experience Google duo is the perfect one.
