What is the main differance then size of cups?

At the risk of sounding like a smart alec but without meaning to: the coins. The larger cups (Midas cups) use America half dollars and are more round, quite reminiscent of a wine flute. The smaller cups (Marlin Cups) use American quarters and the sides are straight. Both end with a production of American dimes.

The quality of both sets is fantastic and the look and feel are very similar, except of course for their size and the cost.