The only drawback is that the these GFDs tend to cost more than the other options. I did on these GFDs, I ended up picking up Outside Loop Computer's Afterburner. One of the reasons is the size and shape of the Afterburner. As you can see, it installs easily and is easy to adjust since you only need to adjust knobs as opposed to dipswitches. It's designed very well with no wires hanging out.
Clock frequency is controlled by two of the switches.
All you need to do is make sure they are set to the same number and you can achieve speeds of 300Mhz all the way to 1050Mhz in increments of 50Mhz. The Afterburner also requires that you plug it into one of your 12V power connectors. You'll have to mess around with the settings to find out what your CPU is capable of achieving. You'll know when you've pushed your Athlon too far. Well, first of all, I made small jumps of 50Mhz and tested each with several loops of 3DMark99, Winstone 99 and Content Creation Winstone 2000 to make sure there weren't any crashes.