Yes, It Works
Bought a vintage Seiko via The Auction Site You Already Know About. Knew it had a few hairline scratches in the crystal, but nothing I couldn't live with, which was before I proceeded to put a non-ignorable large scratch in said crystal. Did the requisite Google search for dealing with mineral-crystal scratches (I think this Seiko was pre-Hardlex by a year or two), and came across a YouTube video demonstrating this very PolyWatch kit, and I immediately ordered said kit. Long-story-short, if works as advertised, but here's pro tip via that YouTube video: you can save yourself a lot of elbow-grease if you (CAREFULLY) use a Dremel tool to apply the pastes included in the kit to the crystal. I followed the suggestions, and was amazed at the results. 100% effective? My mileage says at least 95%, and that's with close inspection. On the day-to-day watch-glance, it's essentially perfect. (Won't work with sapphire crystals, but in theory, you'd never need to worry about sapphire unless you shattered it, no?) Highly recommended.
Rating: 5 stars