I would not recommend them for bulking! Those people modelling for the TV-shop commercial did not use this ****, they used free weights.
* You will not develop stabilizing muscles in the same way as lifting
* The resistance will not be enough for you if you want to bulk. Think about lifting a 250 lbs weight and getting current through your muscle, you would need a car battery yanked up your ass to get that effect.
* It will take a ****load of time to train all the muscles since you will only be doing isolation training instead of compound training.
* Training at gym isn't just about getting bigger muscles, it is a test on personal determination, pushing your limits with weights so you can push the limits everywhere else in life. If you can lift a heavy challenging weight, you will feel everything around you, all problems will be easier to face.
That is the drawback I find with them, I have not tried them so I only speak in my opinion why I haven't bought them.