Master, before enginuity.org's forums disappeared, someone did a comparison of the newfangled not-quite-narrowband AFR sensor to a LC-1. The results weren't in perfect agreement, but they weren't bad either. IIRC, the worst error was ~0.08 near 11:1 where it stopped reading.
Obviously a true narrowband (which is what that graph looks like) would be useless as you say. Are you sure that still applies to the newer cars?