On paper, it sounds great. Last I checked, there were some issues though.
- Google is constantly making that harder. For example, people running GrapheneOS are facing more issues every year. This doesn't seem like a long term solution. More like a temporary workaround.
- Some android apps on Sailfish OS and GrapheneOS don't work properly, because the app knows it's not in a vanilla Android environment.
So, if you want to use your favorite calculator on Sailfish OS or GrapheneOS, it's probably fine. If you want to use a banking app in order to verify your identity to the tax office, it might not work at all, because those apps tend to be very picky. Also, you'll need the same verification thing when interacting with other government agencies, so this isn't just a fun little bonus either. Come to think of it, any office or company that asks for your ID is on this list.
BTW, the bank I use announced a few years ago that they will start phasing out physical code booklets. Good luck living in the 2020s if you still rely on tech from the 1990s. If only we had GrapheneOS or Saislifhs OS in 2005, it would have been awesome. The problem is, the world has moved on.