I my first Motiv ball was Raptor P7, and now about 80% of my arsenal is Motiv, including the three balls you referenced. What impressed me about their line-up is that they pay as much attention to the low end as their premium stuff. I have multiple sanctioned 300's with the solid Assent. How many lower end $100 balls can you throw with real confidence??
My Primal Rage and Venom Toxin are drill pin above ring, and the Frenzy is pin below ring. They all provide a different look, so I don't feel I have any useless overlap. The Rage is a backend monster, the Toxin more of a tamed down version of the Rage, and the Frenzy provides a nice controlled midlane reaction. As much as I like the Venom Toxin, if I was you I might have gone with the Venom Strike instead to get a feel for Motiv solid reactive covers, but you still have a good starting three.
Hopefully you'll find your own success with their line-up.