I own one for my Samsung plus own some anti microbial kitchen products and placemats and honestly can’t tell how anyone would possibly notice a difference.
I let a friend’s child play with my Pixel 2 phone in its ordinary fabric case while she had a bad cold and was an absolute mess. I was teaching her to take photos with it. I washed and rinsed the case and wiped down the phone when she was done with it for the day. I did not catch her cold because I’d already had the antibodies for it. Also, I didn’t touch my face.
Had I not already had the antibodies, I would have caught her cold because I always do if it’s a new germ. I know plenty of people would have expected the fabric case to be problematic. But it wasn’t because there are other factors at play.
I’d be surprised if anti microbial material made a whole lot of difference for a phone case when so much else factors into the equation.
When I was a bank teller, customers came in sick all the time. They’d cough and sneeze. It was gross when you’d see them cough and sneeze right onto the money then hand it to you. But none of us ever got sick from that. First, we had a bullet resistant glass shield that protected us from all the airborne stuff. Secondly, we all knew money is grubby dirty stuff. Our hands were often blackened with it after an hour. So we never ever touched our faces until we washed our hands.
The only way I got sick there was if an employee came in sick after catching something from their family.