Install It If You're Concerned About Security
If you're concerned with security (and who isn't these days), you'll want to think about installing the Nexus Marshmallow update on your device. Android 6.0 comes with some important patches and some new features that will help you protect your smartphone or tablet.
The Android 6.0 Marshmallow update comes with a ton of security fixes including patches from an October Android 5.1.1 Lollipop update. If you haven't installed the August or September Android 5.1.1 security updates, Android 6.0 will bring those patches to you as well.
In addition to these fixes, the Marshmallow update also features improved Permissions and native fingerprint support for an additional layer of security. It's not perfect but it's an improvement over Google's Lollipop operating system.