don't you think aluminum is too soft for a skid plate, and will fatigue fairly quickly?
for offroud I think is too soft, but for daily use is good, and composite will be fine too.
Aluminum does just fine for a daily driver or road race type car. I would not recomend it for rally racing though. Its primarily to prevent oil pan failure for things like unseen speed bumps and such. Its 1/4" thick at the bend/lowest point of impact and the reversed ramp shape will cause the car to "slide" over the obstruction rather then the point of impact being a vertical wall that is your oil pan. Coming off a dirt jump and landing on small boulder is not this skidplates purpose.
skidplate will not help you if you hit big stone. Better try google and will see how WRC skidplate looks like. In my country rally teams use 4-7mm skid plates (sometimes with subframe).