is it worth it? yes, always best to know what your car is doing.
you need a wideband setup and most have a narrow band output on them for the ecu.
you must make sure that you get a good one, as if they are inaccurate then you'll be worrying over nothing.
i have two and both read the same from different manufacturers, but i'd recommend innovate or vems, although the innovate is easier to install.