Good prequel! 
I enjoyed this one a lot and found it even more interesting than the black witch. (And much better than wandfasted). I think it's partly because Sage isn't as slow as Elloren. I grew partial to Elloren with time but Sage is a much more relatable chatacter, and generally needs less character growth for you to respect her. 
It's been a while since I read a third book of a fantasy series and still felt excited to keep going, but I really do! The author of this series does a good job of keeping the hype and excitement going without annoying cliffhangers. 

I will say the speed of the relationship in this one is rather unbelievable. But at least they go for it instead of the angsty "we can't be together because it'll endanger our families" because that got old in the other storyline. 

I've got the shadow wand on hold so I'll continue with the series once it's available.