I've been using the FetHead for about three years and... honestly, it could be better.
It was working pretty well in the beginning, doing its job, no distortion, highs or lows boost, reasonable product for the price. But after about 2 years of using it the contact isn't as snug as it used to be, causing my mic to produce only static noise when moved.
Simply put, great for beginners, does its job, but sadly not great longetivity in my specific case.