> Out of curiosity, have you found any downsides with that setup long-term? Battery health or missed notifications, for example?

Yeah, it is inconvenient to bring two phones. That's definitely a downside. Battery health is fine. I never missed any notifications so far.

I sell them or give to family.

> Not trying to promote anything here — genuinely interested in how people approach this.

Adding this makes me think you do want to promote something.

I used to keep one as a sort of backup internet connection, since there are "unlimited 4 hours of internet" prepaid plans, like $1, here that work pretty well when used as an access point if your home internet's down for whatever reason.

Nowadays I just sell them

Another phone is an audiobook listening device for my kids (they choose and I play).

Of course I also have a dedicated dev phone.

    Secondary camera (with OpenCam) *oss

    Security camera (various software)

    Alarm clock with custom audio files (tibetan bells make a very unobtrusive wakeup sound)

    Guitar tuner & general audio                      recorder

    Mp3 player while working in harsh environments 

Just yesterday I learned the Echo Show 5 can be pwned so I dug mine out, put LineageOS on it, and now it's a satellite for my HA server. Her name is Janet now.

A little bit of @hnburnsy's answer, with segmented logins and emails separated by phones with layered restoration so it's difficult to accidentally get bricked by having one system get malware, system faults, or other failures. Two-Factor Auth also gets separated around between devices.