Ranked in these QuestionsQuestion Ranking
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 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 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.
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.