I certainly think that any exercise is better than nothing.  However upon years of lifting, reading all the magazine, all the online resources, being around many athletes and bodybuilders, I can provide some valuable information.
    1. Nothing works forever.
        The human body adapts and gets use to things so you must always never be doing the same routine for more than 6 weeks.
        Doing super slow is a great thing to do 6 weeks a year at the very most.  Isometrics or static are great to use as well.
        Negatives (eccentrics) are great, but there is a mental /physical connection.  The guys I know that have had the most success with super slow, use such intensity that only 1 set is necessary after warmup(s).  It is so intense that you can be mentality fatigued and overtrain thus cortisol problem.  Vitamin C and Leucine ( 1 of the BCAA') are recommended.
        
        Tom
        AbundaLife

Tom is right in how adaptable the human body is.  However, if one is still making progress on a program, it can be continued past 6 weeks.  I know several powerlifters (including myself) who have made progress on the same routine for 3 months.  You have to listen to your body.
Debi
Grand Rapids, MI