I had the same question as you did. I asked around people, including the guy who runs www.flyers-it.com.
They said that they are from the same manufacturer. Diamond .3 was first introduced at the price US$140 but raised it afterwards. I think because there wasn't anybody selling it. After I got the Flyers-pit lens and compared with my friends' diamond .3, I couldn't find any difference.It's 100% same.