I have been using one for about a year and a half. I don't use it as much as I should but once or twice a week it helps me get through the mid afternoon lull. I

I have been using one for about a year and a half. I don't use it as much as I should but once or twice a week it helps me get through the mid afternoon lull. I find that if I am loosing focus that standing for 20 minutes gets me back on track.