The Flying Goose brand is the most common here in Germany. The Huy Fong brand hasn't been available for a few years after the EU implemented some restriction on one of the ingredients.
My fride, my pantry and my local Asian shops would respectfully disagree with that statement.
Hui Fong Sriracha is less sweet, less garlicky, brighter and the chillies come out way more. It's not the same product as the Flying Goose brand and they certainly can't be substituted for each other. I love 'em both.