I picked up a Gemini and a Cosmo second hand because I was really fascinated by the lineage of the Psion 5 to these devices. I haven't put Linux on the Gemini yet, but I got it on the Cosmo and while running from the internal eMMC I was seeing some issues where the KDE screensaver/unlock seemed to hang, once I got rid of KDE and switched to i3 I haven't had that issue with i3lock.

I also installed UBports which turned out to be WAY easier than I expected, and it works pretty well though the touch first interface isn't optimal on the keyboard first Cosmo.

After I got i3 going I decided I wanted to see about Gemian from SD, and it took a little bit, but I was able to get it working, though I used the TWRP slot so I don't think I'll be able to get cellular working in the SD installation, see below for details.

One thing that sort of sucks is there are 4 slots on the eMMC for bootloaders and the first seems to be Android+Recovery, the second is pre-labeled TWRP by the Cosmo Linux installer, the 3rd and 4th are regular BOOT partitions. I currently have Android, Gemian_SD, KDE_Gemian, UBports in the slots, but UBports is interesting in that it shares the "userdata" with Gemian, and the rootfs lives in the root of the Gemian install and is pointed to by its bootloader.

When it comes to the cellular communications, with the Cosmo Linux you have to use an alternate connection manager because NetworkManager apparently doesn't do the ofono setup properly, but I haven't really had much luck with the cellular in Linux.

So far I've been pretty happy with the wifi only functionality of the SD install, and I'm hoping to use that as sort of a playground to avoid wearing out the eMMC while experimenting, and then I am going to try and backup my configuration changes and migrate them to one of the "regular" boot slots and test it out with cellular (also need to swap my Fi data only SIM to a voice+sms+data one to properly test the full functionality).

One other thing to note is the CoDi software which allows you to use the outer touchscreen as a touchpad is interesting, but definitely could use more tuning because it seems to be fairly slow, not sure if it is the "bus" between the display (has its own STM32 CPU iirc) and the primary CPU/system, or if it is just the CoDi server that is written in Python that is slowing things down a bit, but it is a really cool option even if a bit awkward in my aging mitts.