I really like my wide band oxygen sensor system.
IMO, you need the recording ability to analyze the data, not just looking at a guage while you try to drive. But glancing at some numbers while driving in the pits or changing throttle settings (street) is useful while recording.

It is just a tool, there is no magic number and every combo will like slightly different numbers; but good ranges are availble. One of the best things I like is confirmation that the change I made actually had the result I was looking for, that doesn't happen 100% of the time. Like changing the jets, sometimes the A/F change is too small to make a difference, or larger than expected. Also, a misfire may not be noticed by the driver, but the spike in A/F shows up on the recording. The recording helps define the A/F change with RPM, throttle position, etc.

Use this tool with all the others to make the best decisions. Spark plug reading, timeslips, etc. even the smell of the exhaust at idle!