Just flashed my old 2012 Nexus 7 with the unofficial LineageOS 14.1 ROM from the latest stock version of Lollipop that I had installed. Performance is better than expected; I would even argue that it’s completely usable. I’ve also noticed that it charges faster.
The only issue I had with the XDA instructions were that the newest version of TWRP didn’t work, so I used an older version. Likely not recommended, but for my use case, it’s fine.
Part of the reason I decided to do this was that I have a Nexus 5 that I got from a random seller on Reddit that had LineageOS preinstalled. It works pretty well, aside from a few lag spikes here and there. It’s stable enough to serve my needs, it feels like a slightly cleaner version of stock Android, and it’s somewhat “deGoogled.”
I’m likely only going to use it for ebooks and some video, but I’m happy to give life to it when I consider it’s mostly been sitting dead in a random drawer for the last few months.
Here’s a small step by step for Windows users, in case you can’t find better instructions anywhere else (see disclaimer at the bottom):
Procure ADB by some means. You can download it using the XDA ADB Installer or by downloading the Android Studio SDK straight from the Android Developer website.
If you go for the XDA installer, press Y for all questions, then you can run ADB from anywhere. If you download the SDK, then once you unzip your file, you should have adb.exe in your new folder.
Enable developer options by tapping Build Number in Settings > About Device a number of times.
Go to Developer Options, then enable Android Debugging/ADB interface. Plug it into your computer. You should get a prompt on your device asking if you want to enable debugging–just press yes.
Copy the necessary TWRP version for your device to the SDK folder (if you downloaded the SDK, otherwise skip).
Open a command prompt/powershell to wherever you saved your TWRP by holding shift and right clicking on white space in your Explorer window. Run:
adb reboot bootloader
WARNING: The following step may be optional will delete all of your data. Make sure to back up everything you can before taking this step, and ideally only do it if you need to do it.
You will arrive at your bootloader screen after a little bit of waiting. Check towards the bottom of any text you see–if your bootloader is locked (it will be in red), then run:
fastboot oem unlock
WARNING, AGAIN: The above step will delete all of your data. Make and keep a backup if you need anything, or in case you softbrick your device.
Once your device is unlocked, or if it was already unlocked, run:
fastboot flash recovery twrp-x.x.x.x-device.img
This should flash your recovery partition with your TWRP image. You can (hopefully) use tab to autocomplete your filename after “twrp”, so do that if possible (i.e. if you have only one twrp image saved). Once done, run:
fastboot boot twrp-x.x.x.x-device.img
And you should boot directly into the TWRP image on your device. Once there, allow it to use elevated permissions, then wipe everything but Internal Storage, and install your custom ROM from your Internal Storage.
Then bam, you should be done. Hopefully. From here I just set up LineageOS.
Disclaimer: I take no responsibility for anyone bricking their devices by following any of the steps provided here–I’m not very experienced with this, but thought it would be interesting to document the way I ended up getting it done in case anyone is stuck.