I am a check pilot with Formation Flight Inc, flying with Falcon Flight. I have the MacFarlane Vernier Assist throttle. It looks like a normal throttle, with no center vernier push button. It is splendid, especially for formation flight.
Why do we shun regular vernier throttles for formation flight? When I'm on the wing, I have my throttle friction way loose, almost completely unscrewed. My right hand NEVER leaves the throttle as a wingman. I'm making minute power changes to maintain precise fore/aft position on my leading aircraft. Having to press and hold a center vernier button on the throttle puts you moments behind the time line for the necessary response to any power change need. Straight vernier throttles are simply a liability/risk on formation flight.
Now, MacFarlane's vernier assist throttle lets you also twist in/twist out small changes in manifold pressure for precise power settings. This comes into play when I am LEADING the flight. As flight lead, I tighten down the throttle friction and set 22" MAP and 2400 RPM...and leave it there. Now I'm a consistent platform. If a wingman needs me to reduce power slightly ("Lead, give me one"), I twist the throttle counterclockwise 1 turn, which on my setup reduces the MAP by 1 inch. I do the same thing automatically if I'm leading a 3- or 4-ship through an echelon turn: I reduce the throttle MAP 1" to give those guys flying the wider arc a chance, then dial it back in when we're rolled out.