Thanks for starting this thread myrefugeisintheLord and thanks to those who've posted photos.
I hadn't considered mounting one on the shifter before reading this thread, but I fitted one yesterday and I love it.
Unlike many, I've used a latching push button (push on / push off) with an indicator light mounted on my vacuum gauge (line of sight), so I'm reminded when it's on or off.
I have two reasons for this:
First, my engine takes a little while to stop. This way I don't have to keep my hand on the shifter until I'm sure it's not going to restart by itself.
Second, I have a long steep hill on my commute where I've had to pulse the brakes to keep speed down while EOCing in the past. Now I can leave the injectors off and use engine braking, keeping the brake vacuum pumped up and charging the battery for free.