I use this product for a little more than half a year before I decide to stop . I truly do feel the burn from the workout , but there be just too many con and I have no significant result even though I use the product for such a long time with workout that last even longer than the 6 minute they recommend . pro : 1 -rrb- the exercise on the dvd be very easy to follow and it include a timer to indicate when to stop . 2 -rrb- you will most likely get sore after the first several day , indicate that you muscle be in fact be work -lrb- not necessarily get result -rrb- . 3 -rrb- the dumbbell have groove on both end to facilitate you handle for the shoulder exercise -lrb- see # 5 in con for handle for triceps and biceps -rrb- . 4 -rrb- no battery ! I think most people assume the shake function be electrical . 5 -rrb- if you buy this directly from the manufacturer , you get a 100 % money-back guarantee , include the shipping and handle cost to send it back . they refund the purchase price of the weight almost immediately . con : 1 -rrb- the dvd be certainly not a $ 15 value . the dvd contain only 3 exercise limit to 3 upper muscle : triceps , biceps , and shoulder all within 6 minute . 2 -rrb- for 6 minute a day , I find the workout to be too easy . I be average-build and I have to work at least 15 minute before I start to get tired . 3 -rrb- the dumbbell itself be very noisy , especially if you be try to get a more intense workout by shake the weight more vigorously . you can even hear the noise when you be watch the exercise on the dvd . additionally , I would often be interrupted several time to keep the noise down from the weight . 4 -rrb- towards the end of you workout , the dumbbell will start to slip out of you hand because the palm of you hand start to sweat . as a result , I have to stop my workout a couple of time to readjust the weight . 5 -rrb- exercise during the triceps and bicep exercise be very awkward . you have to wrap one hand around the middle of the weight during these exercise , but it be difficult to hold on to the middle while you be shake . therefore , the weight be design more for shoulder exercise . 6 -rrb- I be sorry to say this , but I definitely look ridiculous when use this product . you would not believe how many people have laugh at I . therefore , you can only use this product if you be by yourself . 7 -rrb- in term of the money-back guarantee if purchase it from the manufacturer , you have to personally make the initiative to contact they and have they refund you for the shipping . unlike the refund for the product , they have still yet to refund I for shipping and handling .