[Moku203]

I wouldn't mind seeing it changed from full immunity because yeah being immune to two damage types, +5 to all stats, a pseudo blind, and if I recall a small stat buff to allies within some range for an evoke is something, but it does come out to it is a full turn and a half, and isn't really useful for any mage unless like you said, you main hand it and off hand like a tome etc. 

but we all know that, I think if it was to lose it's immunity 25 is quite low for it's investment, I'd say at least 50% Light/Dark resist would fit better, and part of me thinks it should be made into a casting tool for Mercalan magic at that point as well, mostly because as Shujin said, most of the point of using it is to lock out those elements, so losing that would make it very pointless for it's M investment.