I have been using viber since 2013. It is a free messenging and calling app. But I am not satisfied by the quality of the video calling. The quality is like 240p or less and it won't work in the low speed Internet connection. The viber consumes also more data than of whatsapp.
Same concept and layout but the viber slower, expensive and slow to load in comparison of same kind of app such as whatsapp and messenger.
The viber is improving but until than its not that useful. And the background data consumption is also their even if I block background data consumption. It automatically uses background data. I don't understand how. The time to load the message is also more and sometime mobile gets hang due to alot of viber messages.
And There are others app which is better than viber. So, I would not recommend this app to use.