I'd be very careful and do a heck of a lot of research before I installed one of those "kits". The research I've done so far shows that introducing a hydrogen flow into you air induction can severely alter the oxygen output of the combustion process which can result in the oxygen sensors reading the engine condition as too lean. This will cause the ECC to boost the mixture to RICH to compensate for the lean condition. This has the effect of not only negating any FE gains, but will drop FE below the pre-install levels.

The solutions available for this problem include trying to trick the Mass Airflow Sensor or replacing the O2 sensors with dummy sensor that tell the ECC lies about exhaust O2 levels.

I have no idea what one of these kits would do the the HCHII's computer system.

Matt in Moore Tafetta White 2008 HCHII