The poignant moment for Tamaki is always seeing people start a journey to know Christ.
"I think there is a preconceived idea in a lot of people's minds about what they think church is, who they think Jesus is and what they think Christians are about, and those are the things that we have to dismantle."
Tamaki believes the church's programmes are about getting to the "root of the problem, interrupting generational behaviour and re-culturing the whole family for a better future".
"You can't hope to eradicate some of these problems if you don't know how to change a life. Our evidence of changed lives is everywhere across this nation and now in Australia, too."
The programmes have reached 2000 people across New Zealand and Australia and have received interest from churches as far afield as Alaska and Asia.
"I think the future is changing. It's moving away from some of the things the church has gotten used to. The church is exploding out of the four walls - it is now in the community."
Tamaki has a goal to reduce prison numbers and recidivism.
His son-in-law, and Man Up New Zealand national director, Caine Warren said the programme had a metamorphosis effect, where people come in as "slug and by the end of you are something beautiful".
Former gang member Toko Kopu (57) is a testament to this, having recently replaced his patch for one of a different kind - "Tu Tangata".
Kopu joined the Mongrel Mob at 15, and rose to become president of an influential Mob chapter.
"My dad was heavy-handed, pretty much beat us out of the house and into the Mob. My older brother ran away first and I followed him [at the age of 12] - he became my father and taught me how to survive."
After decades in and out of prison, the programme was suggested to Kopu by a former Mongrel member in 2016 and he has "never looked back".
He has a much better relationship with his wife and daughter, who was born while he was in jail.
"It has given me tools to love again - the addiction of P took that away. It taught me how to be a man, step up for my family and my change has caused a ripple effect."
He has even gone as far as to recruit other Mongrel Mob members.