I used to use the push/pull on off switch by Dubro for years. I had also heard rumors of instances where the switch turned off due to vibration. I didn't believe them until I had it happened to me. I was running a pattern plane secured by the tail in the run-up area. At some point I lost throttle control, shut the engine down manually, and then discovered the switch was off. Happened again. We then tried again a third time and actually watched the pull/push switch slowly walk itself out to off. I stopped using them from then on. You could not have convinced me that this was possible, but it was.
Kurt