Helmet Fire:
The problem with low-inertia heads is that you simply MUST dump the lever at the very first suspicion of trouble. I don't want to restart a well-trodden thread, but at max power in the climb in an R22 you're said to have 1.1 seconds before the rrpm reaches an unrecoverable level in case of engine failure, if you do nothing.
Let's not start another puerile argument about why everyone should be flying something bigger... but let's not encourage people who hear a low rrpm warning horn to look at the gauge before they react.
The time it takes you to look in at the clocks is time wasted. If the engine goes (except in autorotation) you'll get a major left kick of the nose, and that's your cue to break your knuckles.
And a bigger Nr gauge is only going to help you make a bigger smoking hole.