Lots of products out there, so in addition to checking out their ads, look for independent product reviews and comparisons as well as checking out the DIY Youtube videos.

I ended up going for the highly regarded and more expensive Osram/Sylvania headlight cleaning kit and would use it again. Biggest downside is it's a multi-step hand rub kit, so a lot more work than many of the other kits. Count on a couple of hours per bulb to do a decent job as well as a pound or two of elbow grease. Not perfect and a lot more manual effort than the others, but done properly the results are decent and I think worth the extra time and cost, plus with their sealer you get a lifetime guarantee that none of the others offer. Cheapest I could find was on Amazon.

Please realize, you're only doing the exterior oxidized and UV damaged plastic. Depending on how bad yours are, up to half the problem can be the back side of the lens and the plastic reflector. The kits will make a significant improvement, but if the results are still unsatisfactory you may wish you'd bit the bullet and just gone for new headlights. That's kind of where I was ending up, but now that I've switched to LEDs I don't need the insides to be any better, in fact if they were any better it would make the LEDs even more bright than they need to be. Getting an Osram kit to do my other 940 is still on my shopping list.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now