I have the originals not the pro flex. They have worked fine for years I have changed the battery in the remote once. That is it, and I use them in uninsulated lacrosse burlys and my feet stay warm all the time. The two things that normally cause problems are not knowing how to properly take care of a rechargeable battery(the batteries on mine are not removable), and using them in boots that are too tight. The insoles do take up a little space so I couldnt just put them in any hunting boot. When these crap out I will definitely buy a set of the newer ones without question.