Tried this over the weekend. Good and bad.
Good, it updated my phone from 13 (maybe 13.1.1, not sure, it had gotten a few versions behind) to 14.0.1 without any direct data loss and it does seem snappier and new security updates are always nice.
Mixed (bad, then better) is that it wasn’t able to mount my internally-formatted sdcard after the update. Rebooted three or four times and it was never able to mount. Finally booted with it unplugged, forgot the sdcard, shut down, reinserted, and then reformatted as internal again, while losing all its prior contents. The better news is that unlike with Android 12 and 13, the reformatted sdcard has consistently mounted on all the reboots since.
Bad (for me personally) is that the Teracube Android 14 had issues with rooting. As soon as I unlock the phone screen after booting up with a rooted boot.img, it crashes and reboots. Eventually I’ll care enough to get a logcat, but for now it just means I can’t plan on using the phone at night courtesy of CF.lumen anymore.
Besides that, I’ve managed to get an angry “why did you lock me up trying to do too much” reboot several times but that’s not new and all in all, it’s seemed to update and behave itself for the most part.