I think the Sony Xperia phones was one of the big proponents of this, where the fingerprint scanner is on the side, integrated into the power button. I never had an Xperia phone but I always thought this was a good idea compared to having it on the back or having it where the home button would be, since when you pick up the phone, your finger should naturally rest on the power button (assuming it’s thoughtfully laid out), and you can also use it when the phone is lying flat on a table, which you can’t do with it on the back.
I know some people are worried about privacy since then you need to use the fingerprint scanner if you want to use the phone, but those people will probably want to buy a non-Android Linux phone like the PinePhone or Librem anyway, and if those get a fingerprint scanner in the future, it will probably have a physical switch that disconnects it electrically, like they do for the cameras.
Personally, I like them over the more common back of the phone location or even the newer under-screen ones, and never under understood why they didn’t take off, but what do you think?
They make a lot of sense and are really nice to use for the most part unless you’re left handed (then you’ll want to scan a different finger/hold the phone a bit differently).
The S10e had one as well and worked quite well, I like them about as much as the rear mounted scanner placement and prefer both to front mounted scanners.
Pine64 is working on a scanner backcover for the PinePhone too, pretty neat addition imo -
teddit.net/r/PINE64official/comments/l40esv/fingerprint_scanner_update_the_new_prototype_is/