Actually this is the problem. The playing surface on a 4.5x9 foot table is 54"x108" not 50x100". 100" is 8'4". But if someone make a table that is 100x50" then it's not conforming to regulation sizes. 50"x100" is more than 8ft and less than a 9ft. In fact it's about 16% less playing surface.
Now a pool table can theoretically be any size that is twice as long as it is wide. But if one thinks that they are buying a 4.5x9ft table then they should measure it to be sure. Don't want someone breaking Mosconi's record only to find out they weren't on the right sized table.
I would bet that the only verbatim knockoffs come from the established large companies like Star Billiards. Yalin probably was making nearly 1:1 copies because now they are Brunswick's partner and manufacturer for China.