Recs.
Updated
SpecsUpdate
Pros
Pro Desktop apps allow texting, calling and enables transferring calls between devices
Viber has native apps for both Windows and Mac that allow you to send and receive messages from your desktop. You can also use the desktop to make and receive calls. Synchronizes between all devices you are using Viber on. Allows transferring calls between devices.
Pro Insight and well documented encryption
Viber has made a documentation available, explaining in great details their encryption system and giving good insight on how it works.
Cons
Con The company evades U. S. tax
The company uses the common practice of tax haven addresses in order to avoid paying US taxes despite being registered in Delaware.
Con Constantly on
Need apps like Greenify to stop it from being constantly on and active, even if you don't use it.
Con Constant reminders of messages
If you don't check your messages (say your in a group chat and simply don't check all of them), it will flood your notifications.
Recommendations
Comments
Flagged Pros + Cons
Con Shady company
There is zero information on the founders of Viber, which leads to some questions as to who is behind a platform that has access to a large swath of user information.
Out of Date Pros + Cons
Con Has multiple a security vulnerabilities
EFF gave Viber's security 1 out of 7 points in November, 2014. It deducted points because the provider is capable of reading encrypted messages, there's no way to verify contacts identities, past communications are not secure if encryption keys are stolen, the code is not open to independent reviews, the security design is not properly documented and there has not been a recent code audit.
Con Potential spyware
Viber communication's aren't end-to-end encrypted. The company has access to the key that the communication's are encrypted with.