This is aimed more at having installs work acceptably out of the box without requiring manual adjustment of the gain (and in the face of SDRs with different frontends). If you’ve got a good manual setting dialled in, that’s better - but the majority of installs don’t do that (for example the OP!)
The default for upgrades of existing installs is to leave your gain setting untouched.
There is also the “burst” adaptive gain which does something that’s not currently possible with manual gain setting (decreasing gain when loud signals are seen); but that’s fairly situational and isn’t on by default.
It can work with other SDRs but currently only the rtlsdr code implements the gain-control hooks needed (and there’s no airspy implementation in mainline dump1090-fa yet)
It is a dump1090-fa feature so if you’re using dump1090-fa you can enable it.
readsb doesn’t implement this.