Thanks to both of you, this was very helpful.
For one thing, the price at Amazon is less then a 10th of what was asked by the ebay seller. This might be justified if one was a genuine article from old times and the other a modern reproduction. But my guess it that it was just preying on the uninformed.
The Amazon page has a link to a modern edition called "Hanayama Portable Large Military Shogi". There one can clearly see the principle of the game: The reverse side of all koma is blank, and this blank side is faced up in the initial setup. It is indeed very similar to Stratego (Which I played a few times. But we preferred Chess or Risk.) But in Stratego you at least see your own pieces. In this original version you have to remember how you set them up.