As a prison abolitionist, I am very sceptical about things like this. Sure, for this Hilter guy it worked and I'm glad it did, still on a whole, more people get radicalized than de-radicalized in prison.
Most prisoners are there for property crimes and the "bad guys" who really hurt people, aren't helped or bettered either. We aren't free until all of us are free. Don't let positive examples like this one cloud your judgment on an overall bad institution like the prison complex. Transformative justice is a much better solution, also for people like this.