When comparing Debian noroot vs UserLAnd, the Slant community recommends UserLAnd for most people. In the question“What are the best ways to run Linux applications on Android?” UserLAnd is ranked 7th while Debian noroot is ranked 12th. The most important reason people chose UserLAnd is:
If you need a X Session vnc gets started with a single click. No configuration needed. Usable on the android host or any other device capable of running vnc.
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Pros
Pro Support for X out of the box
If you need a X Session vnc gets started with a single click. No configuration needed. Usable on the android host or any other device capable of running vnc.
Pro No root needed
You get a full Linux environment without the need to root your device.
Pro Easy setup
No longer than 5 minutes and you have a full blown XFCE desktop running.
Pro Free and Open Source
Like Termux - UserLAnd is an entirely open source application - the developers are responsive on Github and actively working on the project.
Cons
Con Android 6.0 not supported
If you have a newer device, this won't work.
Con Can't reinstall after uninstall on Android 4.4 or older
Deleting the app data is possible though. That will free most of the memory.
Con Requires at least 900 megabytes of internal storage
It cannot be installed on the SD card. That's a lot of storage considering it only works on pre-Marshmallow (Android 6) phones.
Con Not supported below Lollipop
This is actually an issue with the programming and having to work around different architectures, but it still really stinks.