I bought two different devices for dumping ROM and save game data, and the one that worked best for me was the insideGadgets GBxCart RW.
I even thought about offering as a service that people could ship their GameBoy carts to me and I would dump the ROM and SAV files for them, and then I would ship their cart back to them and provide the dumped data along with a video showing the process of dumping the data.
Here are some relevant notes and pictures of mine about that subject
https://text.nstr.no/~erik.nordstrom/game_boy_color_forever....
https://casa.nstr.no/0001
I bought two different devices for dumping ROM and save game data, and the one that worked best for me was the insideGadgets GBxCart RW.
I even thought about offering as a service that people could ship their GameBoy carts to me and I would dump the ROM and SAV files for them, and then I would ship their cart back to them and provide the dumped data along with a video showing the process of dumping the data.