Just noticed an ad in last month's AS&T for new Saxon 12" Dobs. AFAIK, the Saxon Dobs are made by Synta? The ad says it's f/4, but the Saxon web site says it's f/5. I'd assume it's a typo in the ad, though it actually looks fairly squat in the photo.
AFAIK, the Skywatchers are Synta-manufactured. I think the Dobs sold by Celestron are also made by Synta, except I'd read somewhere that the 12" one uses a GSO mirror.