I fitted the Touratech version to my girlfriend's F650GS a few weeks ago. It looks good and it stops the spray coming up through the instrument panel void and getting your neck/face wet (I am talking about motorbikes honest!).
It doesn't keep much crap off the engine - you need to fashion a mudguard flap/extender to do that.
From memory, the version on the F650 site was more of a short protector for the rear shock fashioned from an oil container which was, coincidently, shaped to fit once cut in half. It did seem a good idea though a quick look on the site has failed to find the article.
Believe it or not but Jon has a great design for fashioning a hugger from the corners of a plastic oil can, don't laugh cos it does work! He's away for a couple of weeks but if you leave him a message I'm sure he'll send details instructions. He might even have posted about it on here.
As for a mud guard extension the 650 Dakars have extensions forward and back which are very effective
This is what was on the F650 site - Not my design, and I can't remember who it was, but I owe them a pint ;
You can get the oil "cans" in black, green, red and grey/silver
I'll add all the pics too;
I recently changed the oil in the car, I bought the oil from Halfords, it's their own brand, 5 litre pack.
When the can was empty, I cut the back of the can out, measured and trimmed it so that it fits between the tyre and swing arm
Held it in place with 2 ty-wraps using the bottom suspension linkage mounts on the underside of the swing arm.
The can had a curve in it so that even when the suspension is compressed it doesn't foul the rear of the petrol tank, and it extends far enough below the swing arm to protect the linkage as well as protecting the shock, it's a cheap but effective means of protection, it's also colour matched silver!
Gavin says "overall height is 12-13 inches, width at widest part 7 inches, the size and shape is basically the same as the back of the oil can.