4/5 stars. Excellent melee unit.
Background.
The Charonites are what you get when you mix regular Ogryns with illegal surgery. Not even the Mechanicum endorses the creation of Charonites, and so they have had to be created by the Saturnyne and Pavonis on Terra. The Mechanicum doesn't like this much at all. At least the conversion process results in strong loyalty and controllable frenzy.
Strengths.
These space ogres are awesome in close combat. With 3 wounds each and T=5=S, they will cause some significant damage. Add on the fact that they have A=4 and you will immediately see why they are rightly considered deadly.
Add on their claws, hammer of wrath, rage, and death frenzy and they are a terror to behold. The weight of their attacks coupled with rending means they can even be a threat to terminators.
Weaknesses.
The main issue I see here is how to get them into position. Their movement rate is not bad at 7 inches, but they have no natural transport options and they are massively bulky. Solve this problem and you're good to go!
Builds.
9 Charonites (360 points).
I've taken the maximum number here. There are no other upgrade options. You probably don't need 36 attacks (i.e., 4x9) base, but if you want something dead in melee, then this will probably just about do the job outside of really elite terminators. They will chew through regular marines with contemptuous ease.