Doesn't work if the current version is incompatible or a new owner. You can't install older versions from the App Store. But there are outside of PlayStore archives on the web of older versions of Android Apps for older prehistoric Androids.
Once Apple has told an App developer that they must only support > version whatever, the app maker does it or the app is pulled. It might otherwise be identical. But now though you can see it in the App store, it won't install. You can still buy music tracks
I don't need the iPhone to be portable without a cord. Though it's possible on some to replace the cell.
If I was worried about ebook compatibility I'd have an iPhone or iPad not too new but still a supported iOS and install anything that MIGHT later be needed, for the day when support is dropped. Maybe an iPhone 8, if the battery is DIY replaceable. The official Apple shop here quotes €90 to replace an iPhone 8 battery. My last phone is excellent, 6", no stupid notches or holes, earphone jack, FM Radio, SD card slot and unlocked for free after 1 year. WiFi and BT and Casting as well as being a phone. €99 Though my older Android 4.3" phone works better on an HDTV as it has as real micro HDMI socket. An adaptor to regular HDMI was €4. It also has a pop-out battery. Not so many Android Apps install on it now.
I use it to test epub ebooks in Aldiko to see that they are OK on a 4.3" screeen. It also has a decent FM radio, 3.5mm jack, SD card, WiFi, BT and is smaller and older than the iPhone 4S with better Mobile reception. The one of the last with Sony-Ericsson branding.