If youve got a good one Rich (ie a decent thickness), they actually protect the swingarm very well in the event of an off..and you can also have the toeguard built into it on some like mine for scrutineering. Swingarm is one of the first bits to touch down on a left hand spill
Weeksy, I've drilled holes into the top of the carbon guard, then the screws which hold the plastic/rubber chain protector (ontop of the swingarm) pass through the swingarm guard and into the already pre-drilled holes, works a treat........
The swingarm cover I had was the perfect shape and just screwed into the same places as the chain guard and on the swingarm just below.
I rate them, I had an off at Rocky and rashed the left hand side of the bike, destroying one of the track panels. The carbon swingarm protector was deeply scraped but the swingarm was completely untouched. It was a reasonably quick off as well. Well worth getting one.