I wouldn't use metal let alone a spiked metal slider. The purpose of the slider is just that to allow the bike to slide. Metal is harder then asphalt, so once it catches on an uneven surface you risk it causing the bike to flip and cause more damage.
Recently having been in a crash where I was on the top side of the bike while it was sliding, I wouldn't have liked for it to start flipping.
Like Strife I've also heard of some instances where even the Delrin sliders caused more damage to the bike. Obviously each wreck is going to be different. Were it not for my bike having slid into another vehicle, I think the damage would have been very minor on my bike.
It slid on the left side for several feet and the fairing showed no damage from the slide with the exception of about a 1" cracked piece where the slider was which might have also been caused by the nose fairing being jammed back up against the side fairings and the slider flipping around when it impacted with the vehicle.
Personally though my only desire of the sliders is to protect from minimal damage like in a stand still tip over. I'm actually seriously considering not getting them at all on my next bike.