Flying Squirrel - Can't comment on H500's ship but, in general, the big concern with an engine overspeed in this model is the lower pulley drive shaft. Overspeed requires an eddy current check.
I've owned a 1998 300C for over two years now (the fuel injected, 3 seater, 950lbs. payload model of the H269 series). The only unscheduled maintenance I've had to perform is:
1) New alternator
2) Starter relay
I also changed out the original starter for a SkyTec high torque starter - highly recommended for the colder months.
The CBi, though not as powerful as the 300C, has extended life limits on more components
Vertical Magazine ran an article last year comparing the R22 and 300Cbi. They calculated the scheduled maintenance to be somewhat less for the 300CBi at 2200 and 4400 hours. They also speculated the downtime is less in the CBi, for scheduled maintenance, attributed to the incremental, local shop performed CBi maintenance vs. R22 return-to-factory overhaul.