While this is a good spell... Its mostly only good in PvP. In PvE its only good when its spammed and it really shouldnt be a spamming spell.
I think it would be cool if it (and other future spells?) functioned like Befoul/Consecrate, but on armor. It casts an obsidian-armor like effect on your armor giving each one an amount of charges with which they can reflect. It would then only have a 10-20% reflect chance for maybe a few charges per piece of armor (one casting puts it on all armor) So now its just a buff you can cast once on yourself and others rather than over and over to be magic immune. Its much more convenient and less overpowered in many situations.
Other armor buffing spells could also then be easier to add ^^