But what is the flexibility and customisation?
For me it is largely to do with widgets, although there is a ton of other stuff you can do which I can't be arsed to learn about like different launchers etc which behave in different ways and are customisable so you can genuinely get your phone to act exactly as you want.
My main thing is that it is very useful to me to have a full page readable diary of the month on my second page - I just swipe left to see everything just as it would look on Google calendar. I find this tons more useful than having to click on the icon. I can also interact with this, add events, change which month is displayed etc. Other widgets display weather forecasts, music stuff, bus and traffic info, what day of my cycle I am on etc. If I want to go to the app, I just tap on the widget but I mostly don't need to.
I like being able to control what's on my screen - so I don't need to have every app icon on my home screens which inevitably means a bunch of folders I never look at. I can just have the ones I want to access all the time and the others are accessible in a different way (one gesture). Because I am running stock android rather than a Samsung or whatever version or indeed iOS, I can uninstall everything I want to. There is absolutely no bloatware on my phone. Everything that is on it is something I want to have on it and find useful or fun.
The back button is one of the things I love about Android that immediately became useful even before I started customising things. If I'm in FB and click on a link that opens in Chrome and want to go back to the FB post, it's one click and it works much better than the equivalent process in iOS.
I have set the phone up to do useful things like mute my phone if I turn it face down (so much easier if in meetings or whatever than having to physically push buttons), turn on Bluetooth (so phone can connect to the car and automatically start playing music) and mute phone call notifications when I start driving - it even sends people an automatic message saying 'I'm driving now, I'll get back to you when I can' if someone calls or messages when I am in the car, turn off Bluetooth and turn phone sound up when I get home. They are all little things but they do make my life better and it is a lot better that all this behaviour is chosen by me so it fits with how I like to run my life. It is all automatic so I never need to remember to do any of it, it just happens.
There are more things that I can't remember off the top of my head I am sure and perhaps Apple has caught up with some of this, but DH doesn't seem to be able to do any of them with his iPhone. Maybe he just can't work his phone properly! Not unlikely, tbh...