Good use of the forum to get input on issues, thanks all. Glad my normal descent approach technique using 125 kts in a B206 or 135 in a AS350 to claw back a few of those precious seconds lost in the climb doesn't have a mast bumping risk. Certainly having a bit of headroom over fast cruise to Vne/Vma, unlike the 407, does offer a small advantage here; OK it's more psychological but still makes me feel better!
Good point on making it quite clear to any students or low timers that if this technique is used, the initial gentle nose over must be virtually imperceptible.
On teetering types it would be interesting to know what actually is thought to be the catastrophic precipitating manoeuvre - was it intentional or accidental abrupt nose over or was it turbulence. I have certainly had occasional cabin/baggage contents bangs in a 206 from presumably momentary 0 (or worse) G in very turbulent conditions over hills, despite being at reduced power. Presumably mast bumping is aggravated by low G with big cyclic input?