Damage Multiplier = damage to sheet metal and tail light rather than just the tail light when you back into a tree/rock/parking meter/overly tall speed bump/whatever. And rather than just bust a tail light, the mounting bracket will likely bend and cause the cover to slam into the sheet metal deep enough to gouge it and bust the tail light that it was supposed to protect.
Other than that...I don't think they look too bad. If my rig had them, I'd prolly leave it on, but I don't think I'd put them on. I'm saving my coin for other stuff.
If you change your mind and want to sell, I can point you to a Lexus glam-site or two -- guys there seem to be interested in stuff like the covers -- you should be able to sell quickly.