is appvn safe

my gf want me to add appvn to my phone. I found some sites ( http://appvn.io/, Appvn ) that say it's a safe and legit thing, but most are sites I've never heard of with reviews written in broken English. It's a Vietnamese app that isn't in the app store. Going by my internet rule "if it seems sketchy, it probably is," it doesn't pass. ybody have any reliable info on it?