IMO, the chrome-molly units look fancy and all, but don't offer the performance edge over a billet alloy unit [with chrome-molly steel insert.

The ring gear on the flywheel [in the link] is also an integral part of the unit, and if you were to damage the ring gear in anyway, as a consequence the whole flywheel becomes somewhat useless. A throw away item.

The billet alloy units also offer the performance edge with improved thermal dissipation properties, but drawing heat away from the friction surfaces. Its basically a heat sink for your clutch assembly.

If your on a budget, but are looking for a little performance edge for street duties, get an A12 cast flywheel lightened.

AASCO Motorsport in the US make and supply alloy flywheels for Nissan /Datsun A-series.