I made today two video calls, one with Viber and one with FaceTime. With Viber I was on wifi, with FaceTime I was on cellular. Although being on cellular, the FaceTime call was better, no delays with video (with Viber I had delays), less more artifacts, sound quality was better.
Based on my FaceTime experience, you feel that the iOS ecosystem is so great, it just works. I don’t know what would happen if I had to switch to Android for some reason. I really don’t.
Speaking of Viber, it opens a general topic: privacy. It is hard to share personal data with a company which is not Apple. From what I have seen, it is hard to trust anybody. Sometimes it is even hard to trust Apple (remember Siri recordings).
When it comes to trust, I have a simple principle: when someone denies something with a (big) self-confidence, you have to question that denial.