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.
Current: 2016 F10 535i xDrive AW w/ Black Dakota, ZMM, ZCW, ZDA, ZDB, ZPP, 688 & Black Grills.
Retired: 2011 E92 M3 -AW
....ED April 29th, 2010
Retired: 2007 E92 335i -Space Gray.....ED Oct 19th, 2006