ITs really simple.

The Narrow band o2 sensor, has NO WIDEBAND SENSOR. SO how could it possibly tell you the accurate A/F Ratio?

Its tapped in off the factory O2 sensor, and all it does is read between WOT an lift throttle or CLosed loop and Open loop. It does NOT tell you A/F Ratio, it tells you when you touch the gas, that is it. Same thing a stock o2 sensor does.

A WIDEBAND is usually something like the AEM UEGO. It is a GAUGE that tells an A/F RATIO an displays it. It comes with a Wideband o2 sensor.

FOr the average person, the AEM UEGO is fine, its cheap, $200-250, easy to install and comes with a cool gauge. Its very accurate too.

For the person thats a little more hardcore, the Innovative is what i prefer because of its datalogging capabilitites. But its $350-400