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The Saint Pro is a more stable verison of the popular Saint. "Pro" is the terminology used by Latitude 64 for the added stability, and not the plastic type. The Saint Pro will offer considerably more fade at the end of the throw. You can crank it into headwinds and trust that it won't turn over at all.
The Latitude 64 Opto Air plastic is incredibly super-durable with a great clear look. The Air plastic contains tiny bubbles that allow the disc to be molded at lightweights. Lightweight discs offer better control and distance.