I have used vivi5 for 3months. Until now the performance is still good. I had uninstall my antivirus app and switch off facebook in exessive battery power section, inside Imanager
No complaint for calling, internet( 3g/4gLte)
No complaint for misic video ( no stops automatically)
No complaint for heating.
No complaint for installing apps.
Im not gamer, so I have no complaint for lag
Yes , even in 4gb of ram android is not free of lag, but overall the phone still good and capable well do multitasking