AFR gauge with o2 sensor worth it or not?

Definitely worth it. Takes a lot of the guess work out of tuning, and provides another safety gauge for you too since it’ll show any kind of combustion issues. Hardest part is realizing that the gauge is more accurate than the carburetor is, so, you can’t make the a/f ratio “perfect” all the time. Which might create EFI envy :p

This is the set up I use, has been working great on my Duster.

Innovate DB Digital Air/Fuel Ratio Gauge with LC-2 Kits 3796