I really hate the modern idea of locking down devices to protect users from themselves. It's my device and I should be allowed to install what I want on it.
Android's better than iOS in that regard, but that doesn't mean it isn't still terrible. Sure, you can sideload apps, but you still can't run as root unless your device's manufacturer allows it. And sure, it might have a built-in file manager, but in newer versions of Android, you can't read/write to /sdcard/Android/data without a separate device.
And this trend is even infecting non-phone devices as well. You can't install extensions on Firefox if they haven't been signed by Mozilla. The only way to disable this restriction is to use a fork or beta version (Developer Edition or Nightly).
We live in the 21st century and have proper APIs to detect features now, we should not be relying on parsing this user-agent string which is 90% legacy-garbage anyways.
I mean, sites blocking compatible browsers is such a common problem that not only do user-agent switcher extensions exist, they're also some of the most popular extensions out there!