The advantage of this system is the guards are light and can be mounted without lugs - which most modern (racing) bikes no longer have. And to be clear, mud-guards are pretty essential for cycling in the UK unless you are choosy about the days you head out! (The upward spray from the road is just as wet and annoying as any rain falling from above.)
The new 2010/11 version has longer extensions - personally I don't find them necessary (although anyone cycling behind me might think otherwise!), but the option is there if wanted.
The downsides of this system are:
* A fiddle to get on and off. No special tools are needed, but patience will come in handy. Can be done in about 10 minutes with practice. I use rubber bands instead of tie-wraps to secure to brake posts - although the tie-wraps can be removed without cutting, in practice I found it impossible to release them.
* Depending on your bike, there is not much space between the frame and the wheel. I have a Trek Madone, and I can fit these with a 25mm tyre but not a 28mm tyre. Carbon racing bikes were not designed with mud-guards in mind!
* It will take some adjustment to ensure the guards are not rubbing on the tyre - in fact small `fur' stickers will contact on the rims to help keep the guards in place without causing too much friction. Once you have loaded and unloaded your bike from the car, chances are all that careful alignment will be gone and the setup will need adjustment again. And once you are off, it is hard to say if the friction pads are working as they should...
* And because of that, and to properly wash the bike, I tend to remove the guards when I can (which I never do on my Galaxy).
So if you have a racing bike without lugs for guards, and you occasionally venture out into the wet (It is only water after all!), then I'd say these are OK, provided you dedicate some time to get them on and off.