I'm a hawk when it comes to checking if my order has shipped, etc, so it would be nice if I could just do it on my phone without having to turn my computer on.
It's probably as safe as using Amazon on your computer
It is safer than most apps (Bezos is a big stickler about **** like that) - as long as you don't lose your phone it is relatively safe.
i've used it and i've had no problems, so id say its safe.
I have used it for many purchases and have not had a problem yet.