hey there,
i have a pair of them and i have to say in the 1st few days i did notice that my legs had a little bit of that "sore muscle" feeling like you have just worked out.now its nothing major but you can feel it.but after the initial first few days i didnt feel that again,but thats not to say they werent working,maybe i just got used to them.
I wouldnt be too pushed to go out and buy another pair,id rather just walk up a few extra hills...