Few issues, it reset the C:\program files\windowsapps permissions and messed up OneNote... had updated all store apps before update, then installed 9879, and it downgraded all the store apps, went to store to update and all but OneNote updated, OneNote kept giving me a 0x80246007... To solve I have to force my local user to be the owner on windowsapps, and OneNote directories, then I had to delete both OneNote directories, and reset WindowsUpdate (net stop wuauserv and bits delete softwaredistribution, net start wuauserv), did a wsreset, then attempt to re-install and it worked. Then also it reset my Trial key of Office 2013 (which was cool, why I am using trial is I do not want to waste my key on alpha build of Windows 10), it also lost it's product key so I had to reset the Windows 10 key and activate it... worked fine after that... still playing with it...