Hi Saugust,
the add you 'found' is actually Australian. The FT-400 & FT-600 as I understand it were basically produced because Australians did not understand/want the gassers with a lid.
They are simply the Summits of the day, without a lid. Some were sold in the USA, not many. But they are fairly common here. They were sold as Summits in the USA, but just as FT-400/FT-600 here.