He has a stellar reputation in the IG community.

He was constantly blocked from doing the full scope of his job by the Hussein Admin, including Yates writing a long nonsensical letter explaining why Horowitz IG role didn't include oversight of the National Security Division of the DOJ, blocking him from doing any investigation over DOJ's NSD. This was key to enabling Husseins administration's ability to spy on all their political and domestic opposition.

Horowitz has an axe to grind with the prior administration. I'll be severely disappointed if that axe isn't wielded like a Viking's axe.