1Password has some nice features (like it reads QR codes off the page and automatically handles 2FA for you, which is clever, but not necessarily the "2" in "2FA" you were hoping for) but it also has a lot of weird UI decisions that make it confusing to use, especially in a shared company environment.
It is a lot better than it was before though, now it's cross-platform (it used to be exclusively AppleSuperiorityComplexWare), but it's still not open source.
Some types of application I prefer light, some dark. But the premise is wrong:
Only if you're using OLED, which most people aren't, and by very little. You could save more battery by using a low-power mode when you don't need all the bells and whistles.
Debatable, different for different people.
That's not objective, it's personal taste :)