I've got the P4Pro Plus here now and I've been searching around inside the Android settings etc for awhile here ... there is no launcher or app drawer... home button defaults to the DJI GO 4 App ... I can get into "settings/apps/all apps" and see there are a bunch of apps already in there that I can't access ... there's android stock browser, Facebook, Screensavers Android Live Wallpapers and widgets, email exchange services, all the apps regarding cell network config, download/file manager etc... all normal vanilla android stuff but very stripped down... maybe 50 apps total compared to what we see in a normal tablet.
Device info:
Model - GL300E
vanilla android lollipop 5.1.1 with a security patch @2015-12-01
Kernel version 3.10.0 - gl300@djiand02-Rd #88
I was able to enable developer options with the old 10 click trick... so I can enable USB debugging and maybe get inside and force a launcher so I can free it up... BUT ... I'm stopping right there for now cuzz I need this for antenna testing at the moment.
Hope this helps