How heavy are these sunglasses?
Less than 2 ounces.

Are they difficult to load with music?
No.  There are clear, easy to understand instructions in the manual.  If you have ever put music on your computer, then you can put it on the sunglasses.

Are they difficult to operate?
The manual has pictures to make it easier to recognize the different functions and range of abilities.  The manuals were written by people who speak English as a first language, not interpreted English that doesn’t always make a lot of sense.  The cheaper versions are imported from China, and so is the instruction manual.