A few days ago, the Windows Insider team pressed the red button for build 10549.4 to go live to Fast ring Insiders.
This build replaces 10536, which was known for having extremely bad battery life and degrading performance, rumored to be because of the Android subsystem included in the build. 10549 promises to fix all that.
My time with the new build has been a great one, with much better battery life and performance all round, and I have tested this on the Microsoft Lumia 535 (1GB RAM) and Nokia Lumia 520 (512MB).
Unfortunately, the only way to get the new build is that you need to be on Windows Phone 8.1 to get that build, due to an upgrade migration bug in 10549. So, for Windows Insiders running an earlier build, you’ll need to downgrade to 8.1 to get back up to 10.
So the question people asking the most, how is it and should I get it? My answer is this: the build is great with new features such as display scaling and a 4th column of tiles on my phone and not forgetting the significant battery life and performance fixes, so my answer is yes, you should get the new build.