I just used the turtle wax kit on one of my headlights. I had replaced the passenger side and wanted the 10 year old drivers side to match it a little better. I'm trying to save money & not replace the drivers side too. All of my fog is on the outside of the lenses. I think the kit worked great for the price. They still don't match (wasn't expecting them to) but at least it's not as noticeable. I recommend lots of time and a nice cool day when trying to do this. It was about 70 outside when I did mine and it was still too hot to take my time. I have leftover solution so I'm going to buy some more fine grit sand paper and try again in the fall.
Some pictures for comparison:
New one:
Old one before:
Old one after:
All in all, worth the money to me and this kit would be great if you just had yellowing. I hope this helps someone who's interested doing theirs.