I found a solution which might work for you. I had exactly the same problem where the code was only returning the Key Index 0 value.
The answer for me was to make sure the selected object in Get Datasmith User Data or Get Datasmith User Data Value for Key was actually an object in my level (not a reference to a file in my Content Browser).
A quick way to test this is to run from Begin Play:
Get All Actors Of Class (set to Static Mesh)
For Each Loop
Get Datasmith User Data Value for Key (type one of your keys)
Print String
From there it should be simple to convert to something which gives the data on a mouse click and extend the outputs to whatever you need. The Example Usage section in the documentation page shows how to do this: