To me they are nothing but a waste of money.... If you already have detailing materials here is what i do.
-Wet sand headlights with 2500 grit sandpaper
-Wash / Dry / Mask
-2 passes with Manzerna SIP (orange pad)
-2 passes with Manzerna Final polish (green Pad)
-LSP of your choice
You will have brand new looking headlights.
Retired: 2011 E92 M3 AW w/ Silver Novillo ZCP, ZTP, ZPP, 494, 6FL, 507, 302 & 415.....ED April 29th, 2010
Retired: 2007 E92 335i -Space Gray, Black Leatherette + Alum, Nav, ZCW, ZSP, PDC, CA & Sunshade.....ED Oct 19th, 2006