Thankfully, there's now a changelog of sorts, common to both PC and Mobile:
- Improved reliability of the Windows Update Agent, shared drives, virtual private network (VPN), clustering, HTTP downloads, Internet Explorer 11, Hyper-V platform, multimedia playback, and Microsoft Edge.
- Improved performance of push and local notifications, Hyper-V platform, and some social media websites using Microsoft Edge.
- Addressed issue where mapping a drive from an elevated command prompt doesn't work with administrator credentials.
- Addressed issue causing movies that were ripped using the transport stream (.ts) format to play without sound in Windows Media Player and the Xbox One Media Player app.
- Addressed issue causing the Movies & TV app on the Xbox to stop working when attempting to play content that was just purchased from the Store.
- Improved support for networks by adding new entries to the Access Point Name (APN) database.
- Addressed issue causing "Print all linked documents" to not work in Internet Explorer 11.
- Addressed issue preventing some users from changing the default download location in Windows 10 Mobile.
- Addressed issue causing unnecessary notifications about fixing Microsoft account in Windows 10 Mobile.
- Addressed additional issues with multimedia, Windows kernel, Windows shell, enterprise security, storage file system, Remote Desktop, core platform, Hyper-V platform, Windows Update for Business, display kernel, near field communication (NFC), input and composition, Bluetooth, Microsoft Lync 2010 compatibility, Windows Storage API, app registration, Trusted Platform Module, Group Policy, Internet Explorer 11, virtual private network (VPN), BitLocker, wireless networking, datacenter networking, Cortana, PowerShell, Active Directory, connection manager and data usage, Microsoft Edge, Windows Recovery Environment, file clustering, Universal Windows Platform (UWP) apps, audio playback settings, DShow Bridge, app compatibility, licensing, cloud infrastructure, domain name system (DNS) server, network controller, USB barcode reader, and Adobe Flash Player.
As usual, these Insiders builds are available to anyone on the Insiders programme, and with a compatible device (think Lumias 550, 650, 950 or those upgraded officially, according to my original chart). The Release Preview ring is definitely the one to be on, since the Fast and Slow* 'rings' are (or are going to be) deep in early-beta 'Redstone 2' land for months.
* In fact, as with the previous build (.187), the 'Slow' ring Insiders also seem to be being pushed this build, but this is a temporary situation - as soon as Redstone 2 is stable enough, 'Slow' ring Insiders will be automatically bumped up. So being on the Slow ring now is a bit of a 'Do I feel lucky' situation!