TL;DR - Doesn't work.
This stuff is the same old buffing compound snake oil 'cure all' that has been around for years. And just like all the same old snake oil 'cure all' that's been around for years, this doesn't work.
I've got enough experience with this to know some things, so play along:
The headlight i used if on a 1 - 10 scale, 1 being brand new, 10 being "sat in junkyard 10 years, so yellowed you can't see if there is a bulb inside it" was a 2-3. There is some hazing, or I wouldn't have tried this product obviously, but it's nothing that you can not see right through, just looks like a small cloud has formed up on the top half of the lense.
Well the simple "clean headlight, dry, apply product to headlight or sponge and rub until headlight is clear" didn't give much of any result on an overall pretty clear assembly.
This is absolutely not going to help yellowed headlights, not even close. Those need the kits that have sandpaper (and ideally use a drill) to actually get that surface off and resurface the top, that's what you're doing with these kits... and buffing compound can't scuff this up enough to take that top layer off.
Anyway, I gave it a shot, it made it a little slicker, but didn't help the problem, The towel is nice and soft though, I hung onto it, the rest is in the trash.