my logic behind this purpose be to have something convenient and fun to keep near the tv so I could tone up a bit while watch tv . I use it a few time but , for the most part , it be a pretty lonely piece of equipment . I like the concept . you be use multiple set of muscle to make the weight shake . if you be shake and do a curl , that intensify the move and will give you better result . I have read review where other complain ghat you have to make the weight shake yourself . personally I never think this be motorize or vibrate and the concept would be useless . you have to put in some effort with exercise . I have also read review about injury . I recommend new buyer watch the dvd that come with it . more than half the exercise in the routine be standard dumbbell movement that DO no require the weight to be shake . the rest you need to keep good form so that you do not go crazy and shake in the wrong position and get a injury . I do not always watch dvd that come with my purchase . I rarely do . in this case , it be necessary to see it once . would I buy this again ? probably because I be curious and do like the concept . would I replace this if it break ? no. . I already multi task enough when I watch tv . it would be easier for I to bring the stability ball and watch do ab exercy or just a plain set of dumbbell . for a novelty piece , it do make a interesting conversation piece .