You need multiple grades of abrasiveness. After done, you need to put a coating on them to protect from future damage.
No. After done, you only need to touch it up. Put a coating on and you are just paying for marketing deception.
A coating does not last either, then you are left having to strip that off and do a full restoration again instead of just minor touchups.
It is very simple. You (or prior owner) lapsed on upkeep, then you make it right, then you can either keep up , or believe marketing nonsense that a special coating you have to strip off is better when it isn't, unless you always park in the direct sun and it's a matter of intervals doing it rather than labor and expense.
If you prefer buying new headlamp housings, that is an option too, and it can vary how difficult to install and align the headlights, and not all are created equal. I'd rather stick with what I have until the reflective surface has degraded.
As always there is something to keep in mind, that if you strive for perfection, it is a fleeting thing and it takes a maximum amount of time or money. Your vanity could cost you and if you want to pay that price, it is the right thing for you to do, but you should stop and think about why you need this, what gap in your life (Or your vision if you are unsafe to drive at night) is this fixing. It is not something that the average person has to jump through hoops to solve.
Consider how many accident reports you've seen where the cause was "headlight lenses weren't clear enough", lol. No, that is ridiculous. There is a very minor speed difference between driving safe for your equipment with perfect new lenses and reasonable aged ones after restored using minimal effort rather than some great proposed marketed "system" to do it.
This is just working materials. You polish, using progressively finer grit depending on where to start, and you seal it with nothing more than polishing sealant you'd use for car paint. Then you have no burden if stripping it off, can just reapply the same polishing sealant. I know this will blow people's minds, that afte the first refinish, you ONLY need to reapply the same polishing sealant on a timely basis as long as you own the vehicle. Some will say you have to do it more often, and yeah, each time you apply that polishing sealant to the rest of the vehicle, do the headlights too. It's kind of funny how easy that is then people try to make it hard.