I have and have used a micron style vacuum guage made by Robinair. It turns out that they are very sensitive to oil or refrigerant contamination.
You are absolutely right about the necessity. Twenty nine inches is not enough and none of the gauges made are accurate enough to tell whether you are doing anything or not. I would guess that around 90% of all evacuations never boil water. You can suck all year long at 29inches and you won't boil water unless it is awful hot out, probably well above 100deg F. I haven't looked at a table in a few years.
The electronic tester was really only good to gauge what type of service level we needed to maintain on our vacuum pumps to be able to achieve the necessary vacuum. They never worked accurately for more than a season.
Bosch Master, ASE Master, L1
33 years MB technician