OK, yobos, I'm bouncing back in for this one... ::015::
I've had the neoprene units - they look great and are useful when you first install them. get them dirt, and I'm talking anything from road grime to offroading, and they trap dirt inside, against your fork tubes. Yes, you can remove them for washing, so that's cutting zip ties every time you wash the bike, wash them out, dry them and rezip tie in place. If that's your process, more power to ya - it's not for me.
I have the Altrider aluminum guards. Easy to install, easy to position if you need to "bend" things slightly. I doubt the soft aluminum will do much damage to the hard forks if they touch, but a valid point. Still a MUCH better option, IMO. I have over a thousand miles on mine in dirt and onroad - narry a twitch from them. Even over...ah...well...at faster speeds, we'll say, they remain rock solid.
Yes, I did drop the bike - no they didn't come close to bending into the fork - could it happen? Yeah, sure, anything is possible, but that might be a small issue compared to other issues if you find yourself front side down hard enough to make that kind of contact.
Bottom line - I spent my money on neoprene, and removed them on both my Tenere and KTM 690 Enduro R. The KTM runs around nekkid now, and Tenere carries the weight of the aluminum guards.