Performance Looking Good
We've been using the Nexus Android Marshmallow update since Developer Preview 1. We've been testing the software on Google's Nexus 6 flagship and thus far, we've found the update to be outstanding in several key areas. That has us extremely excited about the public Android 6.0 release.
We haven't experienced any major issues with the update and battery life has held up since the final beta release. We don't expect the update to be flawless but the fact that it's performing this well ahead of release is a great sign.
At this point, we aren't recommending the Developer Preview 3 to anyone. Now that we're just a few short weeks away from release, you're better off waiting for the public release. If you want feedback, take a look at our review. It's a great starting point.