ok, rcvd quite some pm asking me why wideband. i'll try to be as layman as possible.
conventional afr gauges or what we called narrow band, or some plp called full throttle tuning only tunes 1/5th to 1/6th of the available map area. Part throttle where you spend most of your driving time and is the most common area for complaints. (poor fuel economy, roughness, stumbling). Some plp said they also use narrowband tuning on dyno but very few dynos are capable holding a constant load for part throttle tuning. Dynos do not accurately represent real world conditions like under-hood airflow at speed and RAM air effects. Typically you car will run leaner off the dyno than on by about 3/10ths of a point. If you are running closed loop and your part throttle fuelling is incorrect, your full throttle fuelling will be affected.
Using a wideband will enable more accurate fuel tuning. Most wideband meters have a 0-5 volt output proportional to air fuel ratio. That output is fed back into the O2 sensor wiring where convert it back into a precise air fuel ratio. The stock O2 sensor is very inaccurate for anything other than 14.7:1 air fuel ratio.
so as a summary, narrowband, as its being called only show your full throttle afr instead of closeloop ratio. Trust me, there is alot of "dancing" happen in between idling and full throttle load.
Think of this way, of you're having a turbo, while ur turbo gradually building up power and its getting leaner as it goes, without having the reading, i will just kaboom your engine and thats is way too late to realise.