I have never used an orb before, so I have no clue what is compatible and what is not.

What shield feats work with orbs? Improved Shield bash, shield mastery...etc

Is it considered a shield for vanguard abilities - to the fore, shield combatant, vicious shield, shield specialization, stunning shield, shield riposte, missile shield, shield charge...etc

What about stalwart defender - overbalance, defensive stance, counterattack

Thanks