Conclusions
The only problem I have with all overclocking cards at present is the price. The components aren't expensive, and although to build and sell hand-held units would be time consuming and warrant a USD$60 price tag I don't know why someone hasn't semi-mass produced them yet for cheaper. Could just be the limited market for them. USD$60 (about A$90) isn't too much to get an extra 150+MHz (better, with newer cores) out of your CPU though, and it's something I would definitely buy even if I did grumble a bit about the price.

These units are all pretty much fine, there's no gaping flaws with any of them - they all have their own advantages. I imagine most people in Australia will go for the NinjaMicro or Northwind because of the ease of availability, similarly with the Paradox for UK-based folk. US-based readers have more choice locally, they may want to try the NorthWind GFD - slightly cheaper than most and unique because it doesn't require a power cable, so there's less cable hassle involved. The K7OC, presuming the dodgy power connector was a one-off, is a decent cheap solution as well and doesn't tie up a power cable because it's a pass-through - it also has the settings printed on the PCB which is good. The Afterburner, while a little more expensive, has dials which make it easy to change and the flat design might make for less cable hassle in your case.

UPDATE: Now, several months after this original roundup was done, the two new contenders from Northwind and ComputerZone are probably the better choice, being smaller, generally running cooler, more easy to configure and not having the compatability problem with KX133 that previous GFD's had. The layouts might be the reason why you choose one over the other, but the much lower pricetag of the ComputerZone unit probably make it the current pick of the lot..

So now, all you Athlon owners really have no excuse not to crank 'em up. :)