they installed those a few years back on I-69 here in Indiana, mainly south towards Indy.
i'd say they work well given the damage i saw to a few sections plus the skid marks on the roadway. looked like it'd stopped some big vehicles given the marks.
the only negatives i've heard are from motorcycle riders. the cables do present a bit of a danger to them. though i think in general a sliding rider/motorcycle is going to go straight under rather than hit a cable.