It's the other way around. Marx by Fleischmann. Didn't know they imported them. As far as value, also don't know. However the set sold for $49.95 in 1961 by Fleischmann.
Marx manufactured HO was defiantly lower quality than rebranded Fleischmann. Many sets were sold through department stores like Sears. Google Marx HO and many images can be found.
Marx made an F3, 0-4-0T, GP9, a Hustler and I believe a Hudson along with freight cars. The F3, Hustler and 0-4-0T (knock-offs of Varney, Athearn and Mantua locomotives) were recently being marketed by Life-Like.
My first HO set in 1963 was a Marx. An 0-4-0T set with 5 cars and oval of stamped tin track on fiber ties and power pack. My mom got it at Sears for 10 bucks as they were clearing out the Christmas stuff.
Many of Marx's HO freight cars are now being sold by Lionel from the purchase of Life-Like.
Rusty