It’s as safe as you make it basically. What I mean by that is that you’re in control of who you give your number to and that app uses your mobile number so if you give it to random people you barely know they can message/call you whatever they want if you get my drift.
I don’t really care about handing my number out like I’m not one of those people who are cautious of it really because at the end of the day if I get strange texts or calls I can just get my service to block their number like it’s no biggie. I speak to rosetyilers via Viber and she’s not a mass murderer so it’s all good and the phone calls are pretty clear as well so honestly don’t be a worry gut it’s totally safe!
Viber is an app similar to whatsapp except you can also make phone calls to anyone across the world completely free (providing you’re connected to wifi or your mobile data)
Honestly it’s awesome and I use it for people who are feeling really down and I can’t reach them e.g if they’re from the US and I’ll often call them or text them or whatever. It’s really good and I highly recommend it.