As far as Android 6.0 Marshmallow updates go, Asus is a laggard. Eight months after Marshmallow was released, Asus only rolled out the update to two of its phones – the ZenFone Laser, in May, and the ZenFone Max in early June. In contrast, Samsung, LG, or even HTC have updates out for a ton of their devices.
The ZenFone Zoom will lose Asus Backup, Google Play Books, Games, and Newsstand, Google+, and ZenFlash. You can still get these apps from the Play Store, if you wish. Factory-resetting the device will rid you of Asus Email, Asus Calendar, Asus Messaging, Asus Browser and Asus Music. Asus points you to Google’s homologous apps for alternatives.
The list of bloatware coming off the ZenFone Selfie after the update is even longer, and includes apps like Mirror, Omlet, and Dr. Eye. Just from their names, it doesn’t sound like you’ll lose much with the update.
We have a full listing of Marshmallow features here, but highlights include Google Now on Tap, Doze mode for improved battery life, and the granular permission model that gives you control over exactly what apps can access on your phone.