Late reply - I have been using SFOS as a daily driver for many years now, on a couple of Sony Xperia 10 III and before that an XA2 Ultra. Everything generally works, although I've had a few problems/niggles:
- I changed the ugly "defaultuser" username over to my name using some hackery
- Internet used to not always work with android apps (fixed)
- IPv6/DNS data leaks when using vpn/wireguard (fixed)
- When I plugged in iems/earbuds with a mic they would always have an annoying buzzing sound, I fixed it by setting up pacat to run as a systemd service (no idea why this worked). Funnily enough I've actually just reflashed SFOS today and this seems to be fixed.
- The keyboard on OSRS doesn't work, which is probably an issue of not having play services/microg.
Apart from that it's generally wonderful. The UI/native apps are miles nicer than Android or iOS, you really can't beat Finnish UI design. It has a small but vibrant community of nerds who make apps for stuff (e.g. Whisperfish for signal or a native kdeconnect client too!) and most of the components are open source.
For native apps I use CHUM or the Harbour, they are generally more updated than the Jolla store and sometimes have better versions (e.g. file explorer with root).
For android I generally use f-droid and aurora store; I don't use microg to save battery but you can if wanted/needed. Battery life is not as good as android but decent enough, it'll last me a day of heavy use/a few of light use.
For me the selling points are you have a phone you can ssh into, way more freedom than android/ios for actually being able to tinker with it as it's basically just a linux machine running a derivative of fedora, and the UI rocks. Plus I trust Jolla far more than a faceless corporation intent on harvesting all your data.
They did have some concerning things regarding Russian investment prior to the Ukrainian war but as far I am aware this has all been dealt with - they filed for bankruptcy then rebranded.
Generally speaking, if you want a Linux phone, you won't find a better choice really.
If you have any questions feel free to reply/pm :)