The 4.5.0.18 update caused no significant issues for me - there are always problems - that’s what this forum is for, but aside from the issues below, I consider it perfectly usable. My perception is that SFOS is steadily improving which each release. Android support works well for what I have tried, and I notice no penalty in speed or power drain. Bluetooth connects to a couple of different cars OK.
I have both Android and SFOS X10iii so I can compare directly.
The X10iii has no 4G VoLTE support in my country on any of the 3 carriers. You can’t make the Android one work, nor the Sailfish one, so this is not a SF issue. This is probably Sony’s doing. This is not an issue if it works in your country, but if it doesn’t 4G voice may never work.
GPS is slow and poor if you are not outside under clear sky. This seems to be an inherent problem with the Sony AOSP. The XA2 had it worse, but I suspect all the Sony’s AOSP suffer from the same underlying issue. This may not matter to you. I need to use GPS in the forest, and it doesn’t work.
Standby power drain is worse than under Android, but the phone is probably good for 2-3 days.