Many have found the release of cumulative updates through the Insider Program to be confusing. After all, most of the devices that support the Windows 10 Mobile Insider Preview don't support the new Fast ring builds, so many were expecting to see these new updates through the Fast ring.
Let's make it clear. Fast ring builds are reserved for Redstone at this point, just like Release Preview builds are reserved for cumulative updates. The Slow ring is currently getting those cumulative updates, but as soon as Microsoft sees a Redstone build that's a bit more stable, that build is likely going to show up on the Slow ring, and the only way to get these cumulative updates will be through Release Preview.
Gabe Aul has also stated numerous times that more devices will be supported in the Redstone builds, once those devices are upgraded to Windows 10 Mobile through the Production ring.
Build 10586.164 does contain a number of fixes. We didn't want to make a hands-on video about it right away. We wanted to take our time and see if it's more stable than previous builds. Check out our hands-on video to see the results.
Make sure to subscribe to Neowin on YouTube! It's the best channel in the universe!