I just ordered one and the way I understood the literature is that the switch to operate the tach was a hold to operate switch and it turned off when released. I would add that I'm not sure about that but did form that assumption when I read it. Sounded like a good idea to me!
That was the original design. David and I suggested that it be a slide switch. As far as I know, it's still a slide switch.
The reason is that when you start the engine, you have to push the button and wait for it to start up. It's not all that bad, but it is irritating. And it's not like the old Tower tach, the battery will run the tach for months sitting in the tool box, and, if you do leave it on and run down the battery, it's a cheap 9V you can get anywhere as opposed to specialty watch batteries that are relatively hard to find, and cost $12. I recall going to half the department stores in Lubbock on a Sunday afternoon trying to find the right kind of watch batteries.
If the new "shiny tube" version has problems, I can suggest some fixes - remove the sensor, remove the tube, remount the sensor on the very front of the box like the original TNC where it belongs, and run leads to connect the sensor to the circuit board. No guarantees, and it might need ferrite beads or something on the longer leads, but it will solve any issue there is with reflections.
Brett