http://www.amazon.com/SKS-Chainboard-Bicycle-Chain-Guard/dp/B001NH1FJENow, I did order it and had it installed on my bike. You will need to take off the crank to install the Guard. I took my bike to my local bike store and had them install it for me. You may want to buy it through the store if you do NOT have a way to remove the crank (And most people do not).
It comes in three sizes, I ordered the largest size for I could not remember if my front largest chain ring was had 42 or 44 teeth. I order the one for 44, but after it was installed I clearly only needed the 42. Thus from the side I can see the teeth of the ring, when it should be covered by the plastic. I have had NO problems with it keeping my pants out of the chain (in that regard it is working) but it is clearly larger then I needed.
Now, I have a three chain ring front crank. I have had no problem with the Chain Guard. It comes with a two notches so that a piece of the Chain Guard can be removed so it can fit around the front derailleur.
As I said above, the front is attached to front hub and the crank is used to keep the Chain Guard in Place. In the rear it has a movable plastic attachment mechanism to attach the Chain Guard to the rear frame. So far it has done all I expected of it.
Here is the chain guard on my Bike:
Notice you can see the chain just at the inner ring of plastic as oppose to where it should be, hidden by that inner ring. More cosmetic then a real problem but something to think about of you decide to get one.