I am using Sailfish OS on a Sony Xperia XA2. I am using it now for about 1 year. Before that I used Sailfish OS on the original Jolla 1 for 5 years. I have also used a Nokia N9 with Meego Linux, which can be considered a forerunner of Jolla/Sailfish.
It uses Qt, Wayland, Systemd. The original Jolla 1 even used Btrfs, which was deemed a mistake. Sailfish OS is available on more devices, like the Pinephone, Fxtec, Cosmo Communicator and others. If you have the official version for Sony Xperia, you get Alien Dalvik, with which you can run Android apps. I am using Whatsapp and Firefox as Android apps this way. I am still hoping that Signal takes off for mesaging, a native app like Whisperfish is something I would really enjoy. With Whatsapp a native app is not possible, there have been threats for lawsuits.
I am very happy with Sailfish, and have been for 6 years. I enjoy having plain linux on my phone, being able to use ssh as root and having a device that I trust. There are some 'costs' involved, like having less shiny bling and less apps available. Companies like Apple and Google can spend billions on their phone platform. Jolla only has about 100 employees in total. You do have to adjust your expectations somewhat.
Jolla have received criticism about not having open sourced all their software. I do understand that criticism, but that argument doesn't make Apple or Google look any better :) I am curious about where linux phones will go in the next years, but currently Sailfish is good for me.
I got my Jolla 1 linux phone in 2013 and I'm still using as my daily driver. And I still love it!
The reason I'm keeping my Jolla 1 phone is that it still gets security updates after 7 years. I also have an Android phone for testing purposes (I sometimes write Android apps and web pages for work), but it only got updates for few years. I don't want to buy a new Android phone if it doesn't get updates after few years. I'll keep my Jolla.
What I remember (not a linux developer) is that sometimes you have to rebalance the filesystem. You can have free space in megabytes, but no inodes left. (If I am wrong someone might correct me). There have been instances, especially later on in its lifecycle, where a system update was aborted due to no space (inodes) which ended in a lot of trouble.
I've been using btrfs as my main file system for about 6 years now and have run into the "no free space" issue about twice.
It's horrible. Everything stops working and freeing space is quite hard.
Other than that I had no issues with it. Subvolumes and snapshots are pretty cool to me, but I can see how the added overhead might not make sense in a processing power and space constrained environment.
Yes, every few months. Communication is not always that clear, the same with the roadmap :) Early in the life of Sailfish it was decided that being behind on upstream software versions was not a problem, since in embedded software things are different then with desktop and server. In the past few years many work has been done to amend this situation.
There are some other factors in play. It is a small company which is short on developers and keeping the system Gecko browser updated has proven to not be very easy. Then there is the issue that some software is closed source, which works fine with Qt 5.6 which is LGPL, but with newer Qt versions it is either full GPL or full commercial. This is a business decision and developers don't have much say in this. What I suspect is happening now is that it gets postponed untill it can no longer be postponed, which does save money :) Then there is the issue that untill now Sailfish was tied to Android drivers and thus is using Android kernels. In that sense the Pinephone is an interesting development with mainlined drivers.
So yes, in the community there are some complaints, but in the real world I can understand it the situation from both sides. For my practical usecase, a daily driver with whatsapp, I haven't seen a better linux phone yet. Again, I am really happy with my phone, even though the situation makes it easy to be critical towards it :)
edit: Oh, just to add to this, updates can last a long time for a hardware iteration. The Jolla 1 from 2013 is still getting updates. Ofcourse the Android layer is not updated due to old Android drivers, but the rest of the system is just the same a the newest hardware that is being supported. I hop my Sony Xperia XA2 from 2018 will last me 5 years as well, or hopefully even longer.
It uses Qt, Wayland, Systemd. The original Jolla 1 even used Btrfs, which was deemed a mistake. Sailfish OS is available on more devices, like the Pinephone, Fxtec, Cosmo Communicator and others. If you have the official version for Sony Xperia, you get Alien Dalvik, with which you can run Android apps. I am using Whatsapp and Firefox as Android apps this way. I am still hoping that Signal takes off for mesaging, a native app like Whisperfish is something I would really enjoy. With Whatsapp a native app is not possible, there have been threats for lawsuits.
I am very happy with Sailfish, and have been for 6 years. I enjoy having plain linux on my phone, being able to use ssh as root and having a device that I trust. There are some 'costs' involved, like having less shiny bling and less apps available. Companies like Apple and Google can spend billions on their phone platform. Jolla only has about 100 employees in total. You do have to adjust your expectations somewhat.
Jolla have received criticism about not having open sourced all their software. I do understand that criticism, but that argument doesn't make Apple or Google look any better :) I am curious about where linux phones will go in the next years, but currently Sailfish is good for me.