Saderma Tuff Toe

Is it just for new boots, or can I use it to repair damaged ones?

It is excellent for both. It is a perfect preventative measure for brand-new boots in high-wear jobs (like roofing or masonry), but it is also highly effective for repairing and sealing toes that have already started to show wear or fraying.

Does it actually stay on, or does it peel off after a few weeks?

When applied correctly, it forms a permanent bond. Because it is a two-part epoxy/polyurethane system that cures into a flexible, solid layer, it is designed to move with the boot rather than cracking or peeling off like cheaper sealants or tapes.