Nope, polywatch is for plastic crystals, not mineral/sapphire. It is not an abrasive per se, it works by "melting" the surface of the crystal and closing the scratch over.
What he needs for mineral/sapphire is the sapphire polishing kit:
Consumables - Drilling, Sanding, Grinding and Polishing. - Watch Bitz Sapphire Crystal polishing kits. - Watchbitz watchmaking tools and supplies
For stainless steel cases Cape Cod is perfect. DO NOT use it on plated (ie: gold plate) watches tho as it will remove the thin layer of plated metal in next to no time. Best thing to clean a plated watch is a micro fibre cloth as it's nice and soft and will not scratch the gold.
You also need to be very careful using it on brushed surfaces as it will polish them up and they will then require re-brushing to restore the finish. The MF cloth and a tooth brush (if necessary) will do the job here as well. A toothbrush is perfect for keeping your bracelets clean too.