A narrow band AFR gauge is actually quite beneficial for all the wrong reasons. First off, it lets you know when you have a good or bad O2 sensor(s). A good O2 sensor will flash back and forth. A bad O2 sensor will stay rich or lean. Before all you nerds out there go out and say that you can always check it's performance with a scanner or with a multimeter, nothing is better than viewing performance on the fly. I want to get some because it always seem like I'm having an O2 issue. I have places to hide my gauges so I don't have to worry about all the flashing lights. Second, if you are trying to get a person to run you, all those flashing lights is a street racer's wet dream so put them on your pillar and watch the rice come in flocks.

In short, only for a testing standpoint and for more attention.