not bad, its working with rubber crap, not weights. i'll stick with regular weights because with that rubber crap you only work out with what resistance you put into it
example;
prettend when you are bench pressing
~the rubber crap
when you start off ;no pressure/weight
when you are one third there you get one third the pressure/weight
when you are two thirds there, you get two thirds the weight
and when you are all the way up, you get the point
so with that the weight changes

with free weights
when you bench press, the weight stays the same

the old fashion ways is always the best :-P