Its a long time since I flew one of "Franks finest" but operationally or even maintenance-wise I don't remember there being any cause to check whether the mags were actually grounded by selecting OFF as I would guess the engine would stop dead as there is no flywheel effect like a prop.
I can understand the requirement with a prop when you see the number of people leaning or standing there with their hand on the prop in so much media. As a maintenance tech it gives me the
shivers - if they only knew. Appears in a lot of so-called "safety" magazines as well.
Mag checks are pretty important in the Robbo and policy was mag check "every" takeoff - no if's or buts. Even if you were on the ground for 30 seconds on all piston types that were operated.
We used to have a policy of cranking to check for a flat cylinder with mags OFF on the first flight of the day which would show up a dud P-Lead. The practice was revised due to subsequent inability to start with crappy little battery and starting issues in the middle of nowhere. It was more important to get a start first time.
No mag drop is the giveaway and yes it is too good to be true - it will always drop.
You gained a "feel" for how good or bad your mags and also plugs were. In the climate we were in mags on R22's might last 300 hours on average before needing some sort of attention. Poor cooling.
I guess as alluded to if one had a dud P-Lead you could start the machine and fly with the mags OFF and in-flight it resurrects itself OOPS! It would need to be the Left one too (I think) as otherwise, I don't think you could start it without
"shower of sparks" and using the retarded mag. The start vibrator grounds the main advanced points (hence P-Lead) and runs the retarded points when the starter is engaged.
As mentioned it is a long time since I flew one of these things but looking at the performance being achieved the aircraft is seriously heavy or the engine isn't producing much power.
I would have thought at 22"-23" and not climbing it doesnt seem to be getting much more than 65-70 knots or is not accelerating ar least. Maybe its me and cant remember just how limited they were!!