At the end of the day, roll with an expansion of your forces that you will enjoy assembling, converting, and painting.
I've found that it can be cool to run forces with a "theme" of sorts... hence why I roll primarily Imperial Armies.
As Scions go, I think those are really nice models. Perhaps you could consider painting them up as Inquisition when working alongside your knights
Again though, make sure you're looking at units you'll enjoy putting together.