Does this work with other belt/pipe mods?

It should work with other mods that change the underground length or add additional belts. Let me know if another mod doesn't seem to work properly.

(Briefly) tested and compatible:
-Bob's
-Ultimate Belts
-Longer Belts Redux
-Krastorio 2

Not fully supported:
-Advanced Fluid Handling (indicators only work in one direction, but it's better than nothing IMO)

Why does the indicator show on the wrong side when placing an underground belt exit?

The indicator always stays "in front" of the belt, so when placing an exit, it'll end up on the wrong side. It is an annoying bug, but is not something I can fix. For a more detailed explanation see this.