Since the Add Armature operator requires you to select some faces, I jumped to the conclusion that the Multi Face Extrude should complete its operation leaving the tips of the extrusions selected.

The following patch seems to accomplish that.

diff --git a/mesh_extra_tools/mesh_mextrude_plus.py b/mesh_extra_tools/mesh_mextrude_plus.py
index ed0ab86..c855f07 100644
--- a/mesh_extra_tools/mesh_mextrude_plus.py
+++ b/mesh_extra_tools/mesh_mextrude_plus.py
@@ -131,6 +131,8 @@ class MExtrude(bpy.types.Operator):
         bm.from_mesh(obj.data)
         sel = [f for f in bm.faces if f.select]
 
+        after = []
+
         # faces loop
         for i, of in enumerate(sel):
             rot = vrot(self, i)
@@ -159,9 +161,14 @@ class MExtrude(bpy.types.Operator):
 
                 bm.faces.remove(of)
                 of = nf
+            after.append(of)
 
         for v in bm.verts: v.select = False
         for e in bm.edges: e.select = False
+
+        for f in after:
+            f.select = True
+
         bm.to_mesh(obj.data)
         obj.data.update()

Unfortunately, while this alteration does allow the Add Armature button to succeed, something weird is going on with the parameters region for the Add Armature operator. Adjusting any of the parameters (such as Max Bones) resets the mesh to the state before Multi Face Extrude was clicked.

If you do any other operation between Multi Face Extrude and Add Armature (such as toggling to edit mode) then the problem does not exhibit itself.

My grip on how adjustments to these operator parameters are handled in the state and the UI is nonexistent, so I'm going to need some help to create a "boundary" between the two operators.

committed part on of the fix, by mutantbob
fix for last face selected thanks purplefrog
rBACea70fe1bab8187b4df8bd8b4aed8314c20b0b441

I have a test version of the addon (parent addon mesh_extra tools) with add armature removed.
I'll allow some more time to try to fix before removing add armature & closing this report.

The problem with the armature is definitely related to the undo system.

If you do
Multi Face Extrude
Add Armature
Undo
then it undo-s both of the operations, not just the Add Armature.

I'm inclined to blame the undo system for the time being.

hi, the current problem with the armature code is the length of the bones, when the addon was working it followed edge loops nicely, now the bone length is incorrect.

hi,
only a few days to go, if anyone can fix the armature length issue, please do, if not, we lose this feature.