Hi Nico,
From what it looks like, you are using an Entity List to render out your list of Products.
If this is the case, then showing related Product information is actually really easy.
The first step will be to create an Entity Form that targets the Product table, with the columns displayed that you would like shown when a Product is selected.
The second step will be to create a new Web Page that has your Entity Form on it (since we want the users to go to a new page rather than open up an Entity Form itself).
Once that is complete, you can setup your Entity List to have a "Details" button which is in the "Options"area, and there should be an option to have the Target Type as Webpage. Once selected, you should be able to pick your web page created in the second step above, and once you give the button a label this will be available to your external users.

Keep in mind, the external users will need Read permission for the Product entity through Entity Permissions or else the button and form will be inaccessible.
If you have any questions please let me know!
Thanks!
Matt Bayes