I have been using this product for years and have always been very satisfied with the results on moderately oxidized fiberglass.  My only complaint was that I couldn't buy a bigger bottle.  Apply this product with a rotary buffer using a woll pad, or by hand with a cotton rag.  I apply it to the pad and then spread it around with the buffer off, before starting at the slowest setting (600rpm on my buffer) and then working up to 1,400rpm.  Buff it out by hand with a clean cotton rag, turning the rag frequently to expose a clean surface.  This is really a cleaner more than a wax. It should be followed by an application of a protective liquid wax (I use 3M Liquid Protective Wax with ScotchGuard).  If you have heavy oxidation, use 3M Restorer Wax instead of this product for your first pass.  You may even wish to do three separate applications; Restorer Wax, followed by Cleaner Wax, and finished with Protective Wax.  Though, if it's really that bad, you'll probably discover your hull is in need of a wet sanding.  This product is a good thing to keep on your boat at all times, along with a couple bags of rags (one for clean, one for dirty), so you can quickly clean spots you notice while you are out enjoying the water, or to touch up at the marina before guests arrive.