I don't have them..i have H&R's but from what i've heard, the intrax springs are harsh. the give a very rough ride.
Also these springs need to be put on with new struts because they will wear out the stock ones quicker then the Eibach's and H&R's because of the stiffness.
This is just what i've heard from the Maxima & Honda people. they might be different for contours