..and if I don't use xposed?
If you don't use Xposed you have to force stop or kill app which draw overlay on screen such as messenger chathead, Lux. Before you grant permission for new app
Sorry for my English though....
Latest update 0.3.3 FC continuously
As far as I know, X Performance's Nougat Beta is beta version of normal commercial firmware.
But concept rom, which lacked most of Sony features, is just an AOSP rom with some Sony app. Mainly for test experimental features and crowdsourcing new ...
If you use xposed, try NoOverlayWarning module.