I'm wondering that too, now. Today I actually tried retrofitting a vindicator knob. It didn't work, so I'm returning it (the green would not completely cover up the red when the valve was fully opened). But what really surprised me is that I'd assumed this would be an idiot proof operation--that the knob physically attached to metal that, when turned, affected air movement elsewhere in the first stage but not at the knob where I was messing around. I found, though, that when opening the valve without the knob apparently being tightened enough, I got high pressure air leakage from by the knob. I don't know enough about my gear to understand that, but I do understand that perhaps making that knob change isn't as innocuous as people may assume.