There are still a lot of capable Android phones out there that do not support Android 6 Marshmallow. I have recently switched to Android from iOS about 2 years ago, and I’ll have to admit that one of the things that drives me mad is the fragmentation.
If you look at the install base for Android 6, you’ll notice that few have installed it. Part of it has to do with over-the-air update issues, and in other cases cell phone companies are to blame. However, the biggest culprit may be that a lot of great legacy Android devices are not supported by google for their latest operating system.
The Nexus 7, LG G4, Galaxy Tab Pro 8.4, LG G3 Verizon, Moto X 2014 to name a few.
Enter CyanogenMod 13. A great way to get Android Marshmallow on the unsupported hardware. Be aware though that you will have to install a nightly build. These releases are still experimental. Install at your own risk.
If you are installing from a previous build, you will have to update your Google apps (Drive etc).
You can grab the experimental nightly builds here.
I had the opportunity to install CyanogenMod on my Nexus 5. I really enjoyed it… most of the time. Every once in a while, my phone would magically reset. It was worth it for the extra features that were there.
Let me know in the comments about your experience with CyanogenMod experimental builds.