cal tracks vs slapper bars

I am sure that some of us older guys have had good luck with slapper bars, i ran a pr on my 64 fury 426 wedge. but that was back in 1968 or so , granted it took a little work to get them to hook. i guess the question i am asking is this, are the cal tracks better on the street or at the track? and what is the advantage over the old style traction bars?. and why do they only work on certian spring combos, and not the others..... this doesnt make sense....