I was looking into the compositor for the first time, but I came across something that is an issue. There seems to be no way to view multiple outputs from the node tree.Both image viewers just show whatever the most recent viewer I clicked on is. Am I correct in this or am I doing something incorrect here?
You’re doing everything right. This is just the way Blender works.
Here’s how you can make it work:
1) In one image editor choose Render Result from the top-down menu. This will show output from the Compositor Node.
2) In the other one choose Viewer Node to see output from selected Viewer Node.
As you noticed, Viewer Node only shows the last selected one. It’s a limitation of Blender.
However, you can use Split Viewer Node node to get side-by-side comparison.
Note: Blender Compositor has some slight limitations, but hey, it’s free :).