The following 3 feats grant a GUARD bonus in the form of an armor bonus:
- Defensive Mastery
- Natural Defense
- Two Weapon Defense
The following 2 feats grant a Guard bonus but does not refer to an armor bonus:
- Extraordinary Defense
- Armor Mastery
There is one feat that has restrictions based on armor bonus:
- Battle Trance
Now that the summary is out of the way, here is the issue. This is the relevant text of Battle Trance:
If your armor bonus is less than 3, it becomes 3.
In current standing, that means that if the bonus from the armor you are wearing + benefits for the first 3 feats listed above is less than 3, it becomes 3. The second two feats would stack.
So, the question is, does this interaction become unnecessarily muddy and confusing for a person building a character because of the use of the term armor bonus rather than Guard directly, and are these interactions what we want?