My wife (she's Korean) uses it ALOT on her phone to talk with 1) our daughter-in-law in Germany, and 2) her Korean friends both in Korea and Hawaii. It works well for her, and the "call" is free!
I have my concerns about a program that is basically called poo-poo talk. Is it predominantly used by fecalphilliacs? Is there a direct line to Mr. Hankey? I think its my dootie to avoid this poo-choo express and not ride the crapicopter. Are the messages stored locally or in the cloud which begs the question: "Where my dookie go?"
It's easy to use app, nothing special, but it does what it promised. Obviously, its not telegram in terms of security, but at the end of the day I think they all cooperate with security agencies.